@@ -27,9 +27,7 @@ The most basic form helper is +form_tag+.
<%end%>
</erb>
When called without arguments like this, it creates a form element that has the current page as its action and "post" as its method (some line breaks added for readability):
Sample output from +form_tag+:
When called without arguments like this, it creates a +<form>+ tag which, when submitted, will POST to the current page. For instance, assuming the current page is +/home/index+, the generated HTML will look like this (some line breaks added for readability):
@@ -41,36 +39,30 @@ Sample output from +form_tag+:
</form>
</html>
If you carefully observe this output, you can see that the helper generated something you didn't specify: a +div+ element with two hidden input elements inside. The first input element with name +utf8+ enforces browsers to properly respect your form's character encoding and is generated for all forms whether action is "get" or "post". Second input element with name +authenticity_token+ is a security feature of Rails called *cross-site request forgery protection* and form helpers generate it for every form whose action is not "get" (provided that this security feature is enabled). You can read more about this in the "Ruby On Rails Security Guide":./security.html#_cross_site_reference_forgery_csrf.
Now, you'll notice that the HTML contains something extra: a +div+ element with two hidden input elements inside. This div is important, because the form cannot be successfully submitted without it. The first input element with name +utf8+ enforces browsers to properly respect your form's character encoding and is generated for all forms whether their actions are "GET" or "POST". The second input element with name +authenticity_token+ is a security feature of Rails called *cross-site request forgery protection*, and form helpers generate it for every non-GET form (provided that this security feature is enabled). You can read more about this in the "Security Guide":./security.html#_cross_site_reference_forgery_csrf.
NOTE: Throughout this guide, this +div+ with the hidden input elements will be stripped away to have clearer code samples.
NOTE: Throughout this guide, the +div+ with the hidden input elements will be excluded from code samples for brevity.
h4. A Generic Search Form
Probably the most minimal form often seen on the web is a search form with a single text input for search terms. This form consists of:
One of the most basic forms you see on the web is a search form. This form contains:
# a form element with "GET" method,
# a label for the input,
# a text input element, and
# a submit element.
IMPORTANT: Always use "GET" as the method for search forms. This allows users to bookmark a specific search and get back to it. More generally Rails encourages you to use the right HTTP verb for an action.
To create this form you will use +form_tag+, +label_tag+, +text_field_tag+, and +submit_tag+, respectively.
A basic search form
To create this form you will use +form_tag+, +label_tag+, +text_field_tag+, and +submit_tag+, respectively. Like this:
<erb>
<%=form_tag(search_path,:method => "get")do%>
<%=form_tag("/search",:method => "get")do%>
<%=label_tag(:q,"Searchfor:")%>
<%=text_field_tag(:q)%>
<%=submit_tag("Search")%>
<%end%>
</erb>
TIP: +search_path+ can be a named route specified in "routes.rb" as: <br/><code>match "search" => "search"</code> This declares that path "/search" will be handled by action "search" belonging to controller "search".
The above view code will result in the following markup:
@@ -80,47 +72,35 @@ The above view code will result in the following markup:
</form>
</html>
TIP: For every form input, an ID attribute is generated from its name ("q" in the example). These IDs can be very useful for CSS styling or manipulation of form controls with JavaScript.
Besides +text_field_tag+ and +submit_tag+, there is a similar helper for _every_ form control in HTML.
TIP: For every form input, an ID attribute is generated from its name ("q" in the example). These IDs can be very useful for CSS styling or manipulation of form controls with JavaScript.
IMPORTANT: Always use "GET" as the method for search forms. This allows users to bookmark a specific search and get back to it. More generally Rails encourages you to use the right HTTP verb for an action.
h4. Multiple Hashes in Form Helper Calls
By now you've seen that the +form_tag+ helper accepts 2 arguments: the path for the action and an options hash. This hash specifies the method of form submission and HTML options such as the form element's class.
The +form_tag+ helper accepts 2 arguments: the path for the action and an options hash. This hash specifies the method of form submission and HTML options such as the form element's class.
As with the +link_to+ helper, the path argument doesn't have to be given a string. It can be a hash of URL parameters that Rails' routing mechanism will turn into a valid URL. However, this is a bad way to pass multiple hashes as method arguments:
As with the +link_to+ helper, the path argument doesn't have to be given a string; it can be a hash of URL parameters recognizable by Rails' routing mechanism, which will turn the hash into a valid URL. However, since both arguments to +form_tag+ are hashes, you can easily run into a problem if you would like to specify both. For instance, let's say you write this:
Here you wanted to pass two hashes, but the Ruby interpreter sees only one hash, so Rails will construct a URL with extraneous parameters. The correct way of passing multiple hashes as arguments is to delimit the first hash (or both hashes) with curly brackets:
Here, +method+ and +class+ are appended to the query string of the generated URL because you even though you mean to write two hashes, you really only specified one. So you need to tell Ruby which is which by delimiting the first hash (or both) with curly brackets. This will generate the HTML you expect:
This is a common pitfall when using form helpers, since many of them accept multiple hashes. So in future, if a helper produces unexpected output, make sure that you have delimited the hash parameters properly.
WARNING: Do not delimit the second hash without doing so with the first hash, otherwise your method invocation will result in an +expecting tASSOC+ syntax error.
h4. Helpers for Generating Form Elements
Rails provides a series of helpers for generating form elements such as checkboxes, text fields and radio buttons. These basic helpers, with names ending in <notextile>_tag</notextile> such as +text_field_tag+ and +check_box_tag+ generate just a single +<input>+ element. The first parameter to these is always the name of the input. In the controller this name will be the key in the +params+ hash used to get the value entered by the user. For example, if the form contains
Rails provides a series of helpers for generating form elements such as checkboxes, text fields, and radio buttons. These basic helpers, with names ending in "_tag" (such as +text_field_tag+ and +check_box_tag+), generate just a single +<input>+ element. The first parameter to these is always the name of the input. When the form is submitted, the name will be passed along with the form data, and will make its way to the +params+ hash in the controller with the value entered by the user for that field. For example, if the form contains +<%=text_field_tag(:query)%>+, then you would be able to get the value of this field in the controller with +params[:query]+.
<erb>
<%=text_field_tag(:query)%>
</erb>
then the controller code should use
<ruby>
params[:query]
</ruby>
to retrieve the value entered by the user. When naming inputs, be aware that Rails uses certain conventions that control whether values are at the top level of the +params+ hash, inside an array or a nested hash and so on. You can read more about them in the parameter_names section. For details on the precise usage of these helpers, please refer to the "API documentation":http://api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html.
When naming inputs, Rails uses certain conventions that make it possible to submit parameters with non-scalar values such as arrays or hashes, which will also be accessible in +params+. You can read more about them in "chapter 7 of this guide":#understanding-parameter-naming-conventions. For details on the precise usage of these helpers, please refer to the "API documentation":http://api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html.
h5. Checkboxes
...
...
@@ -133,7 +113,7 @@ Checkboxes are form controls that give the user a set of options they can enable
The second parameter to +check_box_tag+ is the value of the input. This is the value that will be submitted by the browser if the checkbox is ticked (i.e. the value that will be present in the +params+ hash). With the above form you would check the value of +params[:pet_dog]+ and +params[:pet_cat]+ to see which pets the user owns.
The first parameter to +check_box_tag+, of course, is the name of the input. The second parameter, naturally, is the value of the input. This value will be included in the form data (and be present in +params+) when the checkbox is checked.
h5. Radio Buttons
Radio buttons, while similar to checkboxes, are controls that specify a set of options in which they are mutually exclusive (i.e. the user can only pick one):
Radio buttons, while similar to checkboxes, are controls that specify a set of options in which they are mutually exclusive (i.e., the user can only pick one):
<erb>
<%=radio_button_tag(:age,"child")%>
...
...
@@ -155,7 +135,7 @@ Radio buttons, while similar to checkboxes, are controls that specify a set of o
As with +check_box_tag+ the second parameter to +radio_button_tag+ is the value of the input. Because these two radio buttons share the same name (age) the user will only be able to select one and +params[:age]+ will contain either "child" or "adult".
As with +check_box_tag+, the second parameter to +radio_button_tag+ is the value of the input. Because these two radio buttons share the same name (age) the user will only be able to select one, and +params[:age]+ will contain either "child" or "adult".
IMPORTANT: Always use labels for each checkbox and radio button. They associate text with a specific option and provide a larger clickable region.
NOTE: Always use labels for checkbox and radio buttons. They associate text with a specific option and make it easier for users to click the inputs by expanding the clickable region.
h4. Other Helpers of Interest
Other form controls worth mentioning are the text area, password input, hidden input, search input, tel input, url input and email input:
Other form controls worth mentioning are textareas, password fields, hidden fields, search fields, telephone fields, URL fields and email fields:
Hidden inputs are not shown to the user, but they hold data like any textual input. Values inside them can be changed with JavaScript. The search, tel, url and email inputs are specified in HTML5 and may receive special handling and/or formatting in some user-agents.
Hidden inputs are not shown to the user but instead hold data like any textual input. Values inside them can be changed with JavaScript.
IMPORTANT: The search, telephone, URL, and email inputs are HTML5 controls. If you require your app to have a consistent experience in older browsers, you will need an HTML5 polyfill (provided by CSS and/or JavaScript). There is definitely "no shortage of solutions for this":https://github.com/Modernizr/Modernizr/wiki/HTML5-Cross-Browser-Polyfills, although a couple of popular tools at the moment are "Modernizr":http://www.modernizr.com/ and "yepnope":http://yepnopejs.com/, which provide a simple way to add functionality based on the presence of detected HTML5 features.
TIP: If you're using password input fields (for any purpose), you might want to configure your application to prevent those parameters from being logged.
TIP: If you're using password input fields (for any purpose), you might want to configure your application to prevent those parameters from being logged. You can learn about this in the "Security Guide":security.html#logging.
This guide covers getting up and running with Ruby on Rails. After reading it, you should be familiar with:
This guide covers getting up and running with Ruby on Rails. After reading it,
you should be familiar with:
* Installing Rails, creating a new Rails application, and connecting your application to a database
* The general layout of a Rails application
...
...
@@ -9,21 +10,32 @@ This guide covers getting up and running with Ruby on Rails. After reading it, y
endprologue.
WARNING. This Guide is based on Rails 3.1. Some of the code shown here will not work in earlier versions of Rails.
WARNING. This Guide is based on Rails 3.1. Some of the code shown here will not
work in earlier versions of Rails.
h3. Guide Assumptions
This guide is designed for beginners who want to get started with a Rails application from scratch. It does not assume that you have any prior experience with Rails. However, to get the most out of it, you need to have some prerequisites installed:
This guide is designed for beginners who want to get started with a Rails
application from scratch. It does not assume that you have any prior experience
with Rails. However, to get the most out of it, you need to have some
prerequisites installed:
* The "Ruby":http://www.ruby-lang.org/en/downloads language version 1.8.7 or higher
TIP: Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails 3.0. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02 though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults on Rails 3.0, so if you want to use Rails 3 with 1.9.x jump on 1.9.2 for smooth sailing.
TIP: Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails
3.0. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02
though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults
on Rails 3.0, so if you want to use Rails 3 with 1.9.x jump on 1.9.2 for smooth
sailing.
* The "RubyGems":http://rubyforge.org/frs/?group_id=126 packaging system
** If you want to learn more about RubyGems, please read the "RubyGems User Guide":http://docs.rubygems.org/read/book/1
* A working installation of the "SQLite3 Database":http://www.sqlite.org
Rails is a web application framework running on the Ruby programming language. If you have no prior experience with Ruby, you will find a very steep learning curve diving straight into Rails. There are some good free resources on the internet for learning Ruby, including:
Rails is a web application framework running on the Ruby programming language.
If you have no prior experience with Ruby, you will find a very steep learning
curve diving straight into Rails. There are some good free resources on the
internet for learning Ruby, including:
* "Mr. Neighborly's Humble Little Ruby Book":http://www.humblelittlerubybook.com
@@ -31,19 +43,32 @@ Rails is a web application framework running on the Ruby programming language. I
h3. What is Rails?
Rails is a web application development framework written in the Ruby language. It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Experienced Rails developers also report that it makes web application development more fun.
Rails is a web application development framework written in the Ruby language.
It is designed to make programming web applications easier by making assumptions
about what every developer needs to get started. It allows you to write less
code while accomplishing more than many other languages and frameworks.
Experienced Rails developers also report that it makes web application
development more fun.
Rails is opinionated software. It makes the assumption that there is a "best" way to do things, and it's designed to encourage that way - and in some cases to discourage alternatives. If you learn "The Rails Way" you'll probably discover a tremendous increase in productivity. If you persist in bringing old habits from other languages to your Rails development, and trying to use patterns you learned elsewhere, you may have a less happy experience.
Rails is opinionated software. It makes the assumption that there is a "best"
way to do things, and it's designed to encourage that way - and in some cases to
discourage alternatives. If you learn "The Rails Way" you'll probably discover a
tremendous increase in productivity. If you persist in bringing old habits from
other languages to your Rails development, and trying to use patterns you
learned elsewhere, you may have a less happy experience.
The Rails philosophy includes several guiding principles:
* DRY - "Don't Repeat Yourself" - suggests that writing the same code over and over again is a bad thing.
* Convention Over Configuration - means that Rails makes assumptions about what you want to do and how you're going to do it, rather than requiring you to specify every little thing through endless configuration files.
* REST is the best pattern for web applications - organizing your application around resources and standard HTTP verbs is the fastest way to go.
* Convention Over Configuration - means that Rails makes assumptions about what you want to do and how you're going to
d o it, rather than requiring you to specify every little thing through endless configuration files.
* REST is the best pattern for web applications - organizing your application around resources and standard HTTP verbs
i s the fastest way to go.
h4. The MVC Architecture
At the core of Rails is the Model, View, Controller architecture, usually just called MVC. MVC benefits include:
At the core of Rails is the Model, View, Controller architecture, usually just
called MVC. MVC benefits include:
* Isolation of business logic from the user interface
* Ease of keeping code DRY
...
...
@@ -51,20 +76,34 @@ At the core of Rails is the Model, View, Controller architecture, usually just c
h5. Models
A model represents the information (data) of the application and the rules to manipulate that data. In the case of Rails, models are primarily used for managing the rules of interaction with a corresponding database table. In most cases, each table in your database will correspond to one model in your application. The bulk of your application's business logic will be concentrated in the models.
A model represents the information (data) of the application and the rules to
manipulate that data. In the case of Rails, models are primarily used for
managing the rules of interaction with a corresponding database table. In most
cases, each table in your database will correspond to one model in your
application. The bulk of your application's business logic will be concentrated
in the models.
h5. Views
Views represent the user interface of your application. In Rails, views are often HTML files with embedded Ruby code that perform tasks related solely to the presentation of the data. Views handle the job of providing data to the web browser or other tool that is used to make requests from your application.
Views represent the user interface of your application. In Rails, views are
often HTML files with embedded Ruby code that perform tasks related solely to
the presentation of the data. Views handle the job of providing data to the web
browser or other tool that is used to make requests from your application.
h5. Controllers
Controllers provide the "glue" between models and views. In Rails, controllers are responsible for processing the incoming requests from the web browser, interrogating the models for data, and passing that data on to the views for presentation.
Controllers provide the "glue" between models and views. In Rails, controllers
are responsible for processing the incoming requests from the web browser,
interrogating the models for data, and passing that data on to the views for
presentation.
h4. The Components of Rails
Rails ships as many individual components. Each of these components are briefly explained below. If you are new to Rails, as you read this section, don't get hung up on the details of each component, as they will be
explained in further detail later. For instance, we will bring up Rack applications, but you don't need to know anything about them to continue with this guide.
Rails ships as many individual components. Each of these components are briefly
explained below. If you are new to Rails, as you read this section, don't get
hung up on the details of each component, as they will be explained in further
detail later. For instance, we will bring up Rack applications, but you don't
need to know anything about them to continue with this guide.
* Action Pack
** Action Controller
...
...
@@ -80,69 +119,104 @@ explained in further detail later. For instance, we will bring up Rack applicat
h5. Action Pack
Action Pack is a single gem that contains Action Controller, Action View and Action Dispatch. The "VC" part of "MVC".
Action Pack is a single gem that contains Action Controller, Action View and
Action Dispatch. The "VC" part of "MVC".
h6. Action Controller
Action Controller is the component that manages the controllers in a Rails application. The Action Controller framework processes incoming requests to a Rails application, extracts parameters, and dispatches them to the intended action. Services provided by Action Controller include session management, template rendering, and redirect management.
Action Controller is the component that manages the controllers in a Rails
application. The Action Controller framework processes incoming requests to a
Rails application, extracts parameters, and dispatches them to the intended
action. Services provided by Action Controller include session management,
template rendering, and redirect management.
h6. Action View
Action View manages the views of your Rails application. It can create both HTML and XML output by default. Action View
manages rendering templates, including nested and partial templates, and includes built-in AJAX support. View templates
are covered in more detail in another guide called "Layouts and Rendering":layouts_and_rendering.html.
Action View manages the views of your Rails application. It can create both HTML
and XML output by default. Action View manages rendering templates, including
nested and partial templates, and includes built-in AJAX support. View
templates are covered in more detail in another guide called "Layouts and
Rendering":layouts_and_rendering.html.
h6. Action Dispatch
Action Dispatch handles routing of web requests and dispatches them as you want, either to your application or any other Rack application. Rack applications are a more advanced topic and are covered in a separate guide called "Rails on Rack":rails_on_rack.html.
Action Dispatch handles routing of web requests and dispatches them as you want,
either to your application or any other Rack application. Rack applications are
a more advanced topic and are covered in a separate guide called "Rails on
Rack":rails_on_rack.html.
h5. Action Mailer
Action Mailer is a framework for building e-mail services. You can use Action Mailer to receive and process incoming email and send simple plain text or complex multipart emails based on flexible templates.
Action Mailer is a framework for building e-mail services. You can use Action
Mailer to receive and process incoming email and send simple plain text or
complex multipart emails based on flexible templates.
h5. Active Model
Active Model provides a defined interface between the Action Pack gem services and Object Relationship Mapping gems such as Active Record. Active Model allows Rails to utilize other ORM frameworks in place of Active Record if your application needs this.
Active Model provides a defined interface between the Action Pack gem services
and Object Relationship Mapping gems such as Active Record. Active Model allows
Rails to utilize other ORM frameworks in place of Active Record if your
application needs this.
h5. Active Record
Active Record is the base for the models in a Rails application. It provides database independence, basic CRUD functionality, advanced finding capabilities, and the ability to relate models to one another, among other services.
Active Record is the base for the models in a Rails application. It provides
and the ability to relate models to one another, among other services.
h5. Active Resource
Active Resource provides a framework for managing the connection between business objects and RESTful web services. It implements a way to map web-based resources to local objects with CRUD semantics.
Active Resource provides a framework for managing the connection between
business objects and RESTful web services. It implements a way to map web-based
resources to local objects with CRUD semantics.
h5. Active Support
Active Support is an extensive collection of utility classes and standard Ruby library extensions that are used in Rails, both by the core code and by your applications.
Active Support is an extensive collection of utility classes and standard Ruby
library extensions that are used in Rails, both by the core code and by your
applications.
h5. Railties
Railties is the core Rails code that builds new Rails applications and glues the various frameworks and plugins together in any Rails application.
Railties is the core Rails code that builds new Rails applications and glues the
various frameworks and plugins together in any Rails application.
h4. REST
Rest stands for Representational State Transfer and is the foundation of the RESTful architecture. This is generally considered to be Roy Fielding's doctoral thesis, "Architectural Styles and the Design of Network-based Software Architectures":http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm. While you can read through the thesis, REST in terms of Rails boils down to two main principles:
Rest stands for Representational State Transfer and is the foundation of the
RESTful architecture. This is generally considered to be Roy Fielding's doctoral
thesis, "Architectural Styles and the Design of Network-based Software
Architectures":http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm. While
you can read through the thesis, REST in terms of Rails boils down to two main
principles:
* Using resource identifiers such as URLs to represent resources.
* Transferring representations of the state of that resource between system components.
For example, to a Rails application a request such as this:
For example, the following HTTP request:
<tt>DELETE /photos/17</tt>
would be understood to refer to a photo resource with the ID of 17, and to indicate a desired action - deleting that resource. REST is a natural style for the architecture of web applications, and Rails hooks into this shielding you from many of the RESTful complexities and browser quirks.
refers to a photo resource with an ID of 17 and indicates an action to be taken
upon it: deletion. REST is a natural web application architecture which Rails
abstracts, shielding you from RESTful complexities and browser quirks.
If you'd like more details on REST as an architectural style, these resources are more approachable than Fielding's thesis:
If you'd like more details on REST as an architectural style, these resources
are more approachable than Fielding's thesis:
* "A Brief Introduction to REST":http://www.infoq.com/articles/rest-introduction by Stefan Tilkov
* "An Introduction to REST":http://bitworking.org/news/373/An-Introduction-to-REST (video tutorial) by Joe Gregorio
* "Representational State Transfer":http://en.wikipedia.org/wiki/Representational_State_Transfer article in Wikipedia
* "How to GET a Cup of Coffee":http://www.infoq.com/articles/webber-rest-workflow by Jim Webber, Savas Parastatidis & Ian Robinson
* "How to GET a Cup of Coffee":http://www.infoq.com/articles/webber-rest-workflow by Jim Webber, Savas Parastatidis &
Ian Robinson
h3. Creating a New Rails Project
If you follow this guide, you'll create a Rails project called <tt>blog</tt>, a (very) simple weblog. Before you can start building the application, you need to make sure that you have Rails itself installed.
If you follow this guide, you'll create a Rails project called <tt>blog</tt>, a
(very) simple weblog. Before you can start building the application, you need to
make sure that you have Rails itself installed.
TIP: The examples below use # and $ to denote terminal prompts. If you are using Windows, your prompt will look something like c:\source_code>
h4. Installing Rails
...
...
@@ -153,13 +227,19 @@ Usually run this as the root user:
# gem install rails
</shell>
TIP. If you're working on Windows, you can quickly install Ruby and Rails with "Rails Installer":http://railsinstaller.org.
TIP. If you're working on Windows, you can quickly install Ruby and Rails with
"Rails Installer":http://railsinstaller.org.
h4. Creating the Blog Application
The best way to use this guide is to follow each step as it happens, no code or step needed to make this example application has been left out, so you can literally follow along step by step. If you need to see the completed code, you can download it from "Getting Started Code":https://github.com/mikel/getting-started-code.
The best way to use this guide is to follow each step as it happens, no code or
step needed to make this example application has been left out, so you can
literally follow along step by step. If you need to see the completed code, you
To begin, open a terminal, navigate to a folder where you have rights to create files, and type:
To begin, open a terminal, navigate to a folder where you have rights to create
files, and type:
<shell>
$ rails new blog
...
...
@@ -167,15 +247,22 @@ $ rails new blog
This will create a Rails application called Blog in a directory called blog.
TIP: You can see all of the switches that the Rails application builder accepts by running <tt>rails new -h</tt>.
TIP: You can see all of the switches that the Rails application builder accepts
by running
<tt>rails new -h</tt>.
After you create the blog application, switch to its folder to continue work directly in that application:
After you create the blog application, switch to its folder to continue work
directly in that application:
<shell>
$ cd blog
</shell>
In any case, Rails will create a folder in your working directory called <tt>blog</tt>. Open up that folder and explore its contents. Most of the work in this tutorial will happen in the <tt>app/</tt> folder, but here's a basic rundown on the function of each folder that Rails creates in a new application by default:
In any case, Rails will create a folder in your working directory called
<tt>blog</tt>. Open up that folder and explore its contents. Most of the work in
this tutorial will happen in the <tt>app/</tt> folder, but here's a basic
rundown on the function of each folder that Rails creates in a new application
by default:
|_.File/Folder|_.Purpose|
|Gemfile|This file allows you to specify what gem dependencies are needed for your Rails application. See section on Bundler, below.|
...
...
@@ -194,20 +281,13 @@ In any case, Rails will create a folder in your working directory called <tt>blo
|tmp/|Temporary files|
|vendor/|A place for all third-party code. In a typical Rails application, this includes Ruby Gems, the Rails source code (if you install it into your project) and plugins containing additional prepackaged functionality.|
h4. Installing the Required Gems
Rails applications manage gem dependencies with "Bundler":http://gembundler.com/v1.0/index.html by default. As we don't need any other gems beyond the ones in the generated +Gemfile+ we can directly run
<shell>
$ bundle install
</shell>
to have them ready.
h4. Configuring a Database
Just about every Rails application will interact with a database. The database to use is specified in a configuration file, +config/database.yml+.
If you open this file in a new Rails application, you'll see a default database configuration using SQLite3. The file contains sections for three different environments in which Rails can run by default:
Just about every Rails application will interact with a database. The database
to use is specified in a configuration file, +config/database.yml+. If you open
this file in a new Rails application, you'll see a default database
configuration using SQLite3. The file contains sections for three different
environments in which Rails can run by default:
* The +development+ environment is used on your development computer as you interact manually with the application.
* The +test+ environment is used to run automated tests.
...
...
@@ -215,9 +295,15 @@ If you open this file in a new Rails application, you'll see a default database
h5. Configuring an SQLite3 Database
Rails comes with built-in support for "SQLite3":http://www.sqlite.org, which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using an SQLite database when creating a new project, but you can always change it later.
Rails comes with built-in support for "SQLite3":http://www.sqlite.org, which is
a lightweight serverless database application. While a busy production
environment may overload SQLite, it works well for development and testing.
Rails defaults to using an SQLite database when creating a new project, but you
can always change it later.
Here's the section of the default configuration file (<tt>config/database.yml</tt>) with connection information for the development environment:
Here's the section of the default configuration file
(<tt>config/database.yml</tt>) with connection information for the development
environment:
<yaml>
development:
...
...
@@ -227,11 +313,17 @@ development:
timeout: 5000
</yaml>
NOTE: In this guide we are using an SQLite3 database for data storage, because it is a zero configuration database that just works. Rails also supports MySQL and PostgreSQL "out of the box", and has plugins for many database systems. If you are using a database in a production environment Rails most likely has an adapter for it.
NOTE: In this guide we are using an SQLite3 database for data storage, because
it is a zero configuration database that just works. Rails also supports MySQL
and PostgreSQL "out of the box", and has plugins for many database systems. If
you are using a database in a production environment Rails most likely has an
adapter for it.
h5. Configuring a MySQL Database
If you choose to use MySQL instead of the shipped SQLite3 database, your +config/database.yml+ will look a little different. Here's the development section:
If you choose to use MySQL instead of the shipped SQLite3 database, your
+config/database.yml+ will look a little different. Here's the development
section:
<yaml>
development:
...
...
@@ -244,11 +336,14 @@ development:
socket: /tmp/mysql.sock
</yaml>
If your development computer's MySQL installation includes a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the +development+ section as appropriate.
If your development computer's MySQL installation includes a root user with an
empty password, this configuration should work for you. Otherwise, change the
username and password in the +development+ section as appropriate.
h5. Configuring a PostgreSQL Database
If you choose to use PostgreSQL, your +config/database.yml+ will be customized to use PostgreSQL databases:
If you choose to use PostgreSQL, your +config/database.yml+ will be customized
to use PostgreSQL databases:
<yaml>
development:
...
...
@@ -262,7 +357,8 @@ development:
h5. Configuring an SQLite3 Database for JRuby Platform
If you choose to use SQLite3 and using JRuby, your +config/database.yml+ will look a little different. Here's the development section:
If you choose to use SQLite3 and using JRuby, your +config/database.yml+ will
look a little different. Here's the development section:
<yaml>
development:
...
...
@@ -272,7 +368,8 @@ development:
h5. Configuring a MySQL Database for JRuby Platform
If you choose to use MySQL and using JRuby, your +config/database.yml+ will look a little different. Here's the development section:
If you choose to use MySQL and using JRuby, your +config/database.yml+ will look
a little different. Here's the development section:
<yaml>
development:
...
...
@@ -284,7 +381,9 @@ development:
h5. Configuring a PostgreSQL Database for JRuby Platform
Finally if you choose to use PostgreSQL and using JRuby, your +config/database.yml+ will look a little different. Here's the development section:
Finally if you choose to use PostgreSQL and using JRuby, your
+config/database.yml+ will look a little different. Here's the development
section:
<yaml>
development:
...
...
@@ -297,51 +396,79 @@ development:
Change the username and password in the +development+ section as appropriate.
TIP: You don't have to update the database configurations manually. If you had a look at the options of application generator, you have seen that one of them is named <tt>--database</tt>. It lets you choose an adapter for couple of most used relational databases. You can even run the generator repeatedly: <tt>cd .. && rails new blog --database=mysql</tt>. When you confirm the overwriting of the +config/database.yml+ file, your application will be configured for MySQL instead of SQLite.
TIP: You don't have to update the database configurations manually. If you look at the
options of the application generator, you will see that one of the options
is named <tt>--database</tt>. This option allows you to choose an adapter from a
list of the most used relational databases. You can even run the generator
repeatedly: <tt>cd .. && rails new blog --database=mysql</tt>. When you confirm the overwriting
of the +config/database.yml+ file, your application will be configured for MySQL
instead of SQLite.
h4. Creating the Database
Now that you have your database configured, it's time to have Rails create an empty database for you. You can do this by running a rake command:
Now that you have your database configured, it's time to have Rails create an
empty database for you. You can do this by running a rake command:
<shell>
$ rake db:create
</shell>
This will create your development and test SQLite3 databases inside the <tt>db/</tt> folder.
This will create your development and test SQLite3 databases inside the
<tt>db/</tt> folder.
TIP: Rake is a general-purpose command-runner that Rails uses for many things. You can see the list of available rake commands in your application by running +rake -T+.
TIP: Rake is a general-purpose command-runner that Rails uses for many things.
You can see the list of available rake commands in your application by running
+rake -T+.
h3. Hello, Rails!
One of the traditional places to start with a new language is by getting some text up on screen quickly. To do this, you need to get your Rails application server running.
One of the traditional places to start with a new language is by getting some
text up on screen quickly. To do this, you need to get your Rails application
server running.
h4. Starting up the Web Server
You actually have a functional Rails application already. To see it, you need to start a web server on your development machine. You can do this by running:
You actually have a functional Rails application already. To see it, you need to
start a web server on your development machine. You can do this by running:
<shell>
$ rails server
</shell>
This will fire up an instance of the WEBrick web server by default (Rails can also use several other web servers). To see your application in action, open a browser window and navigate to "http://localhost:3000":http://localhost:3000. You should see Rails' default information page:
This will fire up an instance of the WEBrick web server by default (Rails can
also use several other web servers). To see your application in action, open a
browser window and navigate to "http://localhost:3000":http://localhost:3000.
TIP: To stop the web server, hit Ctrl+C in the terminal window where it's running. In development mode, Rails does not generally require you to stop the server; changes you make in files will be automatically picked up by the server.
TIP: To stop the web server, hit Ctrl+C in the terminal window where it's
running. In development mode, Rails does not generally require you to stop the
server; changes you make in files will be automatically picked up by the server.
The "Welcome Aboard" page is the _smoke test_ for a new Rails application: it makes sure that you have your software configured correctly enough to serve a page. You can also click on the _About your application’s environment_ link to see a summary of your application's environment.
The "Welcome Aboard" page is the _smoke test_ for a new Rails application: it
makes sure that you have your software configured correctly enough to serve a
page. You can also click on the _About your application’s environment_ link to
see a summary of your application's environment.
h4. Say "Hello", Rails
To get Rails saying "Hello", you need to create at minimum a controller and a view. Fortunately, you can do that in a single command. Enter this command in your terminal:
To get Rails saying "Hello", you need to create at minimum a controller and a
view. Fortunately, you can do that in a single command. Enter this command in
your terminal:
<shell>
$ rails generate controller home index
</shell>
TIP: If you're on Windows, or your Ruby is set up in some non-standard fashion, you may need to explicitly pass Rails +rails+ commands to Ruby: <tt>ruby \path\to\your\application\script\rails generate controller home index</tt>.
TIP: If you get a command not found error when running this command, you
need to explicitly pass Rails +rails+ commands to Ruby: <tt>ruby
\path\to\your\application\script\rails generate controller home index</tt>.
Rails will create several files for you, including +app/views/home/index.html.erb+. This is the template that will be used to display the results of the +index+ action (method) in the +home+ controller. Open this file in your text editor and edit it to contain a single line of code:
Rails will create several files for you, including
+app/views/home/index.html.erb+. This is the template that will be used to
display the results of the +index+ action (method) in the +home+ controller.
Open this file in your text editor and edit it to contain a single line of code:
<codeclass="html">
<h1>Hello, Rails!</h1>
...
...
@@ -349,17 +476,30 @@ Rails will create several files for you, including +app/views/home/index.html.er
h4. Setting the Application Home Page
Now that we have made the controller and view, we need to tell Rails when we want "Hello Rails" to show up. In our case, we want it to show up when we navigate to the root URL of our site, "http://localhost:3000":http://localhost:3000, instead of the "Welcome Aboard" smoke test.
Now that we have made the controller and view, we need to tell Rails when we
want "Hello Rails" to show up. In our case, we want it to show up when we
navigate to the root URL of our site,
"http://localhost:3000":http://localhost:3000, instead of the "Welcome Aboard"
smoke test.
The first step to doing this is to delete the default page from your application:
The first step to doing this is to delete the default page from your
application:
<shell>
$ rm public/index.html
</shell>
We need to do this as Rails will deliver any static file in the +public+ directory in preference to any dynamic content we generate from the controllers.
We need to do this as Rails will deliver any static file in the +public+
directory in preference to any dynamic content we generate from the controllers.
Now, you have to tell Rails where your actual home page is located. Open the file +config/routes.rb+ in your editor. This is your application's _routing file_ which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions. This file contains many sample routes on commented lines, and one of them actually shows you how to connect the root of your site to a specific controller and action. Find the line beginning with +root :to+, uncomment it and change it like the following:
Now, you have to tell Rails where your actual home page is located. Open the
file +config/routes.rb+ in your editor. This is your application's _routing
file_ which holds entries in a special DSL (domain-specific language) that tells
Rails how to connect incoming requests to controllers and actions. This file
contains many sample routes on commented lines, and one of them actually shows
you how to connect the root of your site to a specific controller and action.
Find the line beginning with +root :to+, uncomment it and change it like the
following:
<ruby>
Blog::Application.routes.draw do
...
...
@@ -370,27 +510,46 @@ Blog::Application.routes.draw do
root :to => "home#index"
</ruby>
The +root :to => "home#index"+ tells Rails to map the root action to the home controller's index action.
The +root :to => "home#index"+ tells Rails to map the root action to the home
controller's index action.
Now if you navigate to "http://localhost:3000":http://localhost:3000 in your browser, you'll see +Hello, Rails!+.
Now if you navigate to "http://localhost:3000":http://localhost:3000 in your
browser, you'll see +Hello, Rails!+.
NOTE. For more information about routing, refer to "Rails Routing from the Outside In":routing.html.
NOTE. For more information about routing, refer to "Rails Routing from the
Outside In":routing.html.
h3. Getting Up and Running Quickly with Scaffolding
Rails _scaffolding_ is a quick way to generate some of the major pieces of an application. If you want to create the models, views, and controllers for a new resource in a single operation, scaffolding is the tool for the job.
Rails _scaffolding_ is a quick way to generate some of the major pieces of an
application. If you want to create the models, views, and controllers for a new
resource in a single operation, scaffolding is the tool for the job.
h3. Creating a Resource
In the case of the blog application, you can start by generating a scaffolded Post resource: this will represent a single blog posting. To do this, enter this command in your terminal:
In the case of the blog application, you can start by generating a scaffolded
Post resource: this will represent a single blog posting. To do this, enter this
command in your terminal:
<shell>
$ rails generate scaffold Post name:string title:string content:text
</shell>
NOTE. While scaffolding will get you up and running quickly, the code it generates is unlikely to be a perfect fit for your application. You'll most probably want to customize the generated code. Many experienced Rails developers avoid scaffolding entirely, preferring to write all or most of their source code from scratch. Rails, however, makes it really simple to customize templates for generated models, controllers, views and other source files. You'll find more information in the "Creating and Customizing Rails Generators & Templates":generators.html guide.
This will create a new database table called posts (plural of Post). The table
will have three columns, name (type string), title (type string) and content
(type text). It will also hook this new database up to Rails (details below).
NOTE. While scaffolding will get you up and running quickly, the code it
generates is unlikely to be a perfect fit for your application. You'll most
probably want to customize the generated code. Many experienced Rails developers
avoid scaffolding entirely, preferring to write all or most of their source code
from scratch. Rails, however, makes it really simple to customize templates for
generated models, controllers, views and other source files. You'll find more
information in the "Creating and Customizing Rails Generators &
Templates":generators.html guide.
The scaffold generator will build 17 files in your application, along with some folders, and edit one more. Here's a quick overview of what it creates:
The scaffold generator will build 17 files in your application, along with some
folders, and edit one more. Here's a quick overview of what it creates:
|_.File |_.Purpose|
|db/migrate/20100207214725_create_posts.rb |Migration to create the posts table in your database (your name will include a different timestamp)|
...
...
@@ -413,9 +572,15 @@ The scaffold generator will build 17 files in your application, along with some
h4. Running a Migration
One of the products of the +rails generate scaffold+ command is a _database migration_. Migrations are Ruby classes that are designed to make it simple to create and modify database tables. Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database. Migration filenames include a timestamp to ensure that they're processed in the order that they were created.
One of the products of the +rails generate scaffold+ command is a _database
migration_. Migrations are Ruby classes that are designed to make it simple to
create and modify database tables. Rails uses rake commands to run migrations,
and it's possible to undo a migration after it's been applied to your database.
Migration filenames include a timestamp to ensure that they're processed in the
order that they were created.
If you look in the +db/migrate/20100207214725_create_posts.rb+ file (remember, yours will have a slightly different name), here's what you'll find:
If you look in the +db/migrate/20100207214725_create_posts.rb+ file (remember,
yours will have a slightly different name), here's what you'll find:
<ruby>
class CreatePosts <ActiveRecord::Migration
...
...
@@ -431,7 +596,14 @@ class CreatePosts < ActiveRecord::Migration
end
</ruby>
The above migration creates a method name +change+ which will be called when you run this migration. The action defined in that method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it at later date. By default, when you run this migration it will creates a +posts+ table with two string columns and a text column. It also creates two timestamp fields to track record creation and updating. More information about Rails migrations can be found in the "Rails Database Migrations":migrations.html guide.
The above migration creates a method name +change+ which will be called when you
run this migration. The action defined in that method is also reversible, which
means Rails knows how to reverse the change made by this migration, in case you
want to reverse it at later date. By default, when you run this migration it
will creates a +posts+ table with two string columns and a text column. It also
creates two timestamp fields to track record creation and updating. More
information about Rails migrations can be found in the "Rails Database
Migrations":migrations.html guide.
At this point, you can use a rake command to run the migration:
...
...
@@ -439,7 +611,8 @@ At this point, you can use a rake command to run the migration:
$ rake db:migrate
</shell>
Rails will execute this migration command and tell you it created the Posts table.
Rails will execute this migration command and tell you it created the Posts
NOTE. Because you're working in the development environment by default, this command will apply to the database defined in the +development+ section of your +config/database.yml+ file. If you would like to execute migrations in other environment, for instance in production, you must explicitly pass it when invoking the command: <tt>rake db:migrate RAILS_ENV=production</tt>.
NOTE. Because you're working in the development environment by default, this
command will apply to the database defined in the +development+ section of your
+config/database.yml+ file. If you would like to execute migrations in other
environment, for instance in production, you must explicitly pass it when
invoking the command: <tt>rake db:migrate RAILS_ENV=production</tt>.
h4. Adding a Link
To hook the posts up to the home page you've already created, you can add a link to the home page. Open +app/views/home/index.html.erb+ and modify it as follows:
To hook the posts up to the home page you've already created, you can add a link
to the home page. Open +app/views/home/index.html.erb+ and modify it as follows:
<ruby>
<h1>Hello, Rails!</h1>
<%=link_to"MyBlog",posts_path%>
</ruby>
The +link_to+ method is one of Rails' built-in view helpers. It creates a hyperlink based on text to display and where to go - in this case, to the path for posts.
The +link_to+ method is one of Rails' built-in view helpers. It creates a
hyperlink based on text to display and where to go - in this case, to the path
for posts.
h4. Working with Posts in the Browser
Now you're ready to start working with posts. To do that, navigate to "http://localhost:3000":http://localhost:3000/ and then click the "My Blog" link:
Now you're ready to start working with posts. To do that, navigate to
"http://localhost:3000":http://localhost:3000/ and then click the "My Blog"
link:
!images/posts_index.png(Posts Index screenshot)!
This is the result of Rails rendering the +index+ view of your posts. There aren't currently any posts in the database, but if you click the +New Post+ link you can create one. After that, you'll find that you can edit posts, look at their details, or destroy them. All of the logic and HTML to handle this was built by the single +rails generate scaffold+ command.
This is the result of Rails rendering the +index+ view of your posts. There
aren't currently any posts in the database, but if you click the +New Post+ link
you can create one. After that, you'll find that you can edit posts, look at
their details, or destroy them. All of the logic and HTML to handle this was
built by the single +rails generate scaffold+ command.
TIP: In development mode (which is what you're working in by default), Rails reloads your application with every browser request, so there's no need to stop and restart the web server.
TIP: In development mode (which is what you're working in by default), Rails
reloads your application with every browser request, so there's no need to stop
and restart the web server.
Congratulations, you're riding the rails! Now it's time to see how it all works.
...
...
@@ -482,11 +670,16 @@ class Post < ActiveRecord::Base
end
</ruby>
There isn't much to this file - but note that the +Post+ class inherits from +ActiveRecord::Base+. Active Record supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another.
There isn't much to this file - but note that the +Post+ class inherits from
+ActiveRecord::Base+. Active Record supplies a great deal of functionality to
your Rails models for free, including basic database CRUD (Create, Read, Update,
Destroy) operations, data validation, as well as sophisticated search support
and the ability to relate multiple models to one another.
h4. Adding Some Validation
Rails includes methods to help you validate the data that you send to models. Open the +app/models/post.rb+ file and edit it:
Rails includes methods to help you validate the data that you send to models.
Open the +app/models/post.rb+ file and edit it:
<ruby>
class Post <ActiveRecord::Base
...
...
@@ -496,17 +689,24 @@ class Post < ActiveRecord::Base
end
</ruby>
These changes will ensure that all posts have a name and a title, and that the title is at least five characters long. Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects.
These changes will ensure that all posts have a name and a title, and that the
title is at least five characters long. Rails can validate a variety of
conditions in a model, including the presence or uniqueness of columns, their
format, and the existence of associated objects.
h4. Using the Console
To see your validations in action, you can use the console. The console is a command-line tool that lets you execute Ruby code in the context of your application:
To see your validations in action, you can use the console. The console is a
command-line tool that lets you execute Ruby code in the context of your
application:
<shell>
$ rails console
</shell>
TIP: The default console will make changes to your database. You can instead open a console that will roll back any changes you make by using +rails console --sandbox+.
TIP: The default console will make changes to your database. You can instead
open a console that will roll back any changes you make by using +rails console
--sandbox+.
After the console loads, you can use it to work with your application's models:
...
...
@@ -523,15 +723,21 @@ After the console loads, you can use it to work with your application's models:
:name=>["can'tbeblank"]}>
</shell>
This code shows creating a new +Post+ instance, attempting to save it and getting +false+ for a return value (indicating that the save failed), and inspecting the +errors+ of the post.
This code shows creating a new +Post+ instance, attempting to save it and
getting +false+ for a return value (indicating that the save failed), and
inspecting the +errors+ of the post.
When you're finished, type +exit+ and hit +return+ to exit the console.
TIP: Unlike the development web server, the console does not automatically load your code afresh for each line. If you make changes to your models while the console is open, type +reload!+ at the console prompt to load them.
TIP: Unlike the development web server, the console does not automatically load
your code afresh for each line. If you make changes to your models while the
console is open, type +reload!+ at the console prompt to load them.
h4. Listing All Posts
The easiest place to start looking at functionality is with the code that lists all posts. Open the file +app/controllers/posts_controller.rb+ and look at the +index+ action:
The easiest place to start looking at functionality is with the code that lists
all posts. Open the file +app/controllers/posts_controller.rb+ and look at the
+index+ action:
<ruby>
def index
...
...
@@ -544,11 +750,19 @@ def index
end
</ruby>
+Post.all+ calls the +Post+ model to return all of the posts currently in the database. The result of this call is an array of posts that we store in an instance variable called +@posts+.
+Post.all+ calls the +Post+ model to return all of the posts currently in the
database. The result of this call is an array of posts that we store in an
instance variable called +@posts+.
TIP: For more information on finding records with Active Record, see "Active Record Query Interface":active_record_querying.html.
TIP: For more information on finding records with Active Record, see "Active
Record Query Interface":active_record_querying.html.
The +respond_to+ block handles both HTML and JSON calls to this action. If you browse to "http://localhost:3000/posts.json":http://localhost:3000/posts.json, you'll see a JSON containing all of the posts. The HTML format looks for a view in +app/views/posts/+ with a name that corresponds to the action name. Rails makes all of the instance variables from the action available to the view. Here's +app/views/posts/index.html.erb+:
The +respond_to+ block handles both HTML and JSON calls to this action. If you
browse to "http://localhost:3000/posts.json":http://localhost:3000/posts.json,
you'll see a JSON containing all of the posts. The HTML format looks for a view
in +app/views/posts/+ with a name that corresponds to the action name. Rails
makes all of the instance variables from the action available to the view.
Here's +app/views/posts/index.html.erb+:
<erb>
<h1>Listing posts</h1>
...
...
@@ -580,18 +794,31 @@ The +respond_to+ block handles both HTML and JSON calls to this action. If you b
<%=link_to'Newpost',new_post_path%>
</erb>
This view iterates over the contents of the +@posts+ array to display content and links. A few things to note in the view:
This view iterates over the contents of the +@posts+ array to display content
and links. A few things to note in the view:
* +link_to+ builds a hyperlink to a particular destination
* +edit_post_path+ and +new_post_path+ are helpers that Rails provides as part of RESTful routing. You'll see a variety of these helpers for the different actions that the controller includes.
NOTE. In previous versions of Rails, you had to use +<%=h post.name %>+ so that any HTML would be escaped before being inserted into the page. In Rails 3.0, this is now the default. To get unescaped HTML, you now use +<%= raw post.name %>+.
NOTE. In previous versions of Rails, you had to use +<%=h post.name %>+ so
that any HTML would be escaped before being inserted into the page. In Rails
3.0, this is now the default. To get unescaped HTML, you now use +<%= raw
post.name %>+.
TIP: For more details on the rendering process, see "Layouts and Rendering in Rails":layouts_and_rendering.html.
TIP: For more details on the rendering process, see "Layouts and Rendering in
Rails":layouts_and_rendering.html.
h4. Customizing the Layout
The view is only part of the story of how HTML is displayed in your web browser. Rails also has the concept of +layouts+, which are containers for views. When Rails renders a view to the browser, it does so by putting the view's HTML into a layout's HTML. In previous versions of Rails, the +rails generate scaffold+ command would automatically create a controller specific layout, like +app/views/layouts/posts.html.erb+, for the posts controller. However this has been changed in Rails 3.0. An application specific +layout+ is used for all the controllers and can be found in +app/views/layouts/application.html.erb+. Open this layout in your editor and modify the +body+ tag:
The view is only part of the story of how HTML is displayed in your web browser.
Rails also has the concept of +layouts+, which are containers for views. When
Rails renders a view to the browser, it does so by putting the view's HTML into
a layout's HTML. In previous versions of Rails, the +rails generate scaffold+
command would automatically create a controller specific layout, like
+app/views/layouts/posts.html.erb+, for the posts controller. However this has
been changed in Rails 3.0. An application specific +layout+ is used for all the
controllers and can be found in +app/views/layouts/application.html.erb+. Open
this layout in your editor and modify the +body+ tag:
<erb>
<!DOCTYPE html>
...
...
@@ -610,11 +837,13 @@ The view is only part of the story of how HTML is displayed in your web browser.
</html>
</erb>
Now when you refresh the +/posts+ page, you'll see a gray background to the page. This same gray background will be used throughout all the views for posts.
Now when you refresh the +/posts+ page, you'll see a gray background to the
page. This same gray background will be used throughout all the views for posts.
h4. Creating New Posts
Creating a new post involves two actions. The first is the +new+ action, which instantiates an empty +Post+ object:
Creating a new post involves two actions. The first is the +new+ action, which
instantiates an empty +Post+ object:
<ruby>
def new
...
...
@@ -637,9 +866,15 @@ The +new.html.erb+ view displays this empty Post to the user:
<%=link_to'Back',posts_path%>
</erb>
The +<%= render 'form' %>+ line is our first introduction to _partials_ in Rails. A partial is a snippet of HTML and Ruby code that can be reused in multiple locations. In this case, the form used to make a new post, is basically identical to a form used to edit a post, both have text fields for the name and title and a text area for the content with a button to make a new post or update the existing post.
The +<%= render 'form' %>+ line is our first introduction to _partials_ in
Rails. A partial is a snippet of HTML and Ruby code that can be reused in
multiple locations. In this case, the form used to make a new post, is basically
identical to a form used to edit a post, both have text fields for the name and
title and a text area for the content with a button to make a new post or update
the existing post.
If you take a look at +views/posts/_form.html.erb+ file, you will see the following:
If you take a look at +views/posts/_form.html.erb+ file, you will see the
following:
<erb>
<%=form_for(@post)do|f|%>
...
...
@@ -672,17 +907,34 @@ If you take a look at +views/posts/_form.html.erb+ file, you will see the follow
<%end%>
</erb>
This partial receives all the instance variables defined in the calling view file, so in this case, the controller assigned the new Post object to +@post+ and so, this is available in both the view and partial as +@post+.
This partial receives all the instance variables defined in the calling view
file, so in this case, the controller assigned the new Post object to +@post+
and so, this is available in both the view and partial as +@post+.
For more information on partials, refer to the "Layouts and Rendering in Rails":layouts_and_rendering.html#using-partials guide.
For more information on partials, refer to the "Layouts and Rendering in
The +form_for+ block is used to create an HTML form. Within this block, you have access to methods to build various controls on the form. For example, +f.text_field :name+ tells Rails to create a text input on the form, and to hook it up to the +name+ attribute of the instance being displayed. You can only use these methods with attributes of the model that the form is based on (in this case +name+, +title+, and +content+). Rails uses +form_for+ in preference to having you write raw HTML because the code is more succinct, and because it explicitly ties the form to a particular model instance.
The +form_for+ block is used to create an HTML form. Within this block, you have
access to methods to build various controls on the form. For example,
+f.text_field :name+ tells Rails to create a text input on the form, and to hook
it up to the +name+ attribute of the instance being displayed. You can only use
these methods with attributes of the model that the form is based on (in this
case +name+, +title+, and +content+). Rails uses +form_for+ in preference to
having you write raw HTML because the code is more succinct, and because it
explicitly ties the form to a particular model instance.
The +form_for+ block is also smart enough to work out if you are doing a _New Post_ or an _Edit Post_ action, and will set the form +action+ tags and submit button names appropriately in the HTML output.
The +form_for+ block is also smart enough to work out if you are doing a _New
Post_ or an _Edit Post_ action, and will set the form +action+ tags and submit
button names appropriately in the HTML output.
TIP: If you need to create an HTML form that displays arbitrary fields, not tied to a model, you should use the +form_tag+ method, which provides shortcuts for building forms that are not necessarily tied to a model instance.
TIP: If you need to create an HTML form that displays arbitrary fields, not tied
to a model, you should use the +form_tag+ method, which provides shortcuts for
building forms that are not necessarily tied to a model instance.
When the user clicks the +Create Post+ button on this form, the browser will send information back to the +create+ method of the controller (Rails knows to call the +create+ method because the form is sent with an HTTP POST request; that's one of the conventions that I mentioned earlier):
When the user clicks the +Create Post+ button on this form, the browser will
send information back to the +create+ method of the controller (Rails knows to
call the +create+ method because the form is sent with an HTTP POST request;
that's one of the conventions that I mentioned earlier):
<ruby>
def create
...
...
@@ -703,15 +955,32 @@ def create
end
</ruby>
The +create+ action instantiates a new Post object from the data supplied by the user on the form, which Rails makes available in the +params+ hash. After successfully saving the new post, +create+ returns the appropriate format that the user has requested (HTML in our case). It then redirects the user to the resulting post +show+ action and sets a notice to the user that the Post was successfully created.
If the post was not successfully saved, due to a validation error, then the controller returns the user back to the +new+ action with any error messages so that the user has the chance to fix the error and try again.
The "Post was successfully created." message is stored inside of the Rails +flash+ hash, (usually just called _the flash_) so that messages can be carried over to another action, providing the user with useful information on the status of their request. In the case of +create+, the user never actually sees any page rendered during the Post creation process, because it immediately redirects to the new Post as soon Rails saves the record. The Flash carries over a message to the next action, so that when the user is redirected back to the +show+ action, they are presented with a message saying "Post was successfully created."
The +create+ action instantiates a new Post object from the data supplied by the
user on the form, which Rails makes available in the +params+ hash. After
successfully saving the new post, +create+ returns the appropriate format that
the user has requested (HTML in our case). It then redirects the user to the
resulting post +show+ action and sets a notice to the user that the Post was
successfully created.
If the post was not successfully saved, due to a validation error, then the
controller returns the user back to the +new+ action with any error messages so
that the user has the chance to fix the error and try again.
The "Post was successfully created." message is stored inside of the Rails
+flash+ hash, (usually just called _the flash_) so that messages can be carried
over to another action, providing the user with useful information on the status
of their request. In the case of +create+, the user never actually sees any page
rendered during the Post creation process, because it immediately redirects to
the new Post as soon Rails saves the record. The Flash carries over a message to
the next action, so that when the user is redirected back to the +show+ action,
they are presented with a message saying "Post was successfully created."
h4. Showing an Individual Post
When you click the +show+ link for a post on the index page, it will bring you to a URL like +http://localhost:3000/posts/1+. Rails interprets this as a call to the +show+ action for the resource, and passes in +1+ as the +:id+ parameter. Here's the +show+ action:
When you click the +show+ link for a post on the index page, it will bring you
to a URL like +http://localhost:3000/posts/1+. Rails interprets this as a call
to the +show+ action for the resource, and passes in +1+ as the +:id+ parameter.
Here's the +show+ action:
<ruby>
def show
...
...
@@ -724,7 +993,9 @@ def show
end
</ruby>
The +show+ action uses +Post.find+ to search for a single record in the database by its id value. After finding the record, Rails displays it by using +show.html.erb+:
The +show+ action uses +Post.find+ to search for a single record in the database
by its id value. After finding the record, Rails displays it by using
+show.html.erb+:
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -751,7 +1022,9 @@ The +show+ action uses +Post.find+ to search for a single record in the database
h4. Editing Posts
Like creating a new post, editing a post is a two-part process. The first step is a request to +edit_post_path(@post)+ with a particular post. This calls the +edit+ action in the controller:
Like creating a new post, editing a post is a two-part process. The first step
is a request to +edit_post_path(@post)+ with a particular post. This calls the
+edit+ action in the controller:
<ruby>
def edit
...
...
@@ -759,7 +1032,8 @@ def edit
end
</ruby>
After finding the requested post, Rails uses the +edit.html.erb+ view to display it:
After finding the requested post, Rails uses the +edit.html.erb+ view to display
it:
<erb>
<h1>Editing post</h1>
...
...
@@ -770,9 +1044,12 @@ After finding the requested post, Rails uses the +edit.html.erb+ view to display
<%=link_to'Back',posts_path%>
</erb>
Again, as with the +new+ action, the +edit+ action is using the +form+ partial, this time however, the form will do a PUT action to the PostsController and the submit button will display "Update Post"
Again, as with the +new+ action, the +edit+ action is using the +form+ partial,
this time however, the form will do a PUT action to the PostsController and the
submit button will display "Update Post"
Submitting the form created by this view will invoke the +update+ action within the controller:
Submitting the form created by this view will invoke the +update+ action within
the controller:
<ruby>
def update
...
...
@@ -792,11 +1069,17 @@ def update
end
</ruby>
In the +update+ action, Rails first uses the +:id+ parameter passed back from the edit view to locate the database record that's being edited. The +update_attributes+ call then takes the rest of the parameters from the request and applies them to this record. If all goes well, the user is redirected to the post's +show+ view. If there are any problems, it's back to the +edit+ view to correct them.
In the +update+ action, Rails first uses the +:id+ parameter passed back from
the edit view to locate the database record that's being edited. The
+update_attributes+ call then takes the rest of the parameters from the request
and applies them to this record. If all goes well, the user is redirected to the
post's +show+ view. If there are any problems, it's back to the +edit+ view to
correct them.
h4. Destroying a Post
Finally, clicking one of the +destroy+ links sends the associated id to the +destroy+ action:
Finally, clicking one of the +destroy+ links sends the associated id to the
+destroy+ action:
<ruby>
def destroy
...
...
@@ -810,15 +1093,25 @@ def destroy
end
</ruby>
The +destroy+ method of an Active Record model instance removes the corresponding record from the database. After that's done, there isn't any record to display, so Rails redirects the user's browser to the index view for the model.
The +destroy+ method of an Active Record model instance removes the
corresponding record from the database. After that's done, there isn't any
record to display, so Rails redirects the user's browser to the index view for
the model.
h3. Adding a Second Model
Now that you've seen how a model built with scaffolding looks like, it's time to add a second model to the application. The second model will handle comments on blog posts.
Now that you've seen how a model built with scaffolding looks like, it's time to
add a second model to the application. The second model will handle comments on
blog posts.
h4. Generating a Model
Models in Rails use a singular name, and their corresponding database tables use a plural name. For the model to hold comments, the convention is to use the name Comment. Even if you don't want to use the entire apparatus set up by scaffolding, most Rails developers still use generators to make things like models and controllers. To create the new model, run this command in your terminal:
Models in Rails use a singular name, and their corresponding database tables use
a plural name. For the model to hold comments, the convention is to use the name
Comment. Even if you don't want to use the entire apparatus set up by
scaffolding, most Rails developers still use generators to make things like
models and controllers. To create the new model, run this command in your
terminal:
<shell>
$ rails generate model Comment commenter:string body:text post:references
...
...
@@ -838,9 +1131,12 @@ class Comment < ActiveRecord::Base
end
</ruby>
This is very similar to the +post.rb+ model that you saw earlier. The difference is the line +belongs_to :post+, which sets up an Active Record _association_. You'll learn a little about associations in the next section of this guide.
This is very similar to the +post.rb+ model that you saw earlier. The difference
is the line +belongs_to :post+, which sets up an Active Record _association_.
You'll learn a little about associations in the next section of this guide.
In addition to the model, Rails has also made a migration to create the corresponding database table:
In addition to the model, Rails has also made a migration to create the
corresponding database table:
<ruby>
class CreateComments <ActiveRecord::Migration
...
...
@@ -858,13 +1154,16 @@ class CreateComments < ActiveRecord::Migration
end
</ruby>
The +t.references+ line sets up a foreign key column for the association between the two models. And the +add_index+ line sets up an index for this association column. Go ahead and run the migration:
The +t.references+ line sets up a foreign key column for the association between
the two models. And the +add_index+ line sets up an index for this association
column. Go ahead and run the migration:
<shell>
$ rake db:migrate
</shell>
Rails is smart enough to only execute the migrations that have not already been run against the current database, so in this case you will just see:
Rails is smart enough to only execute the migrations that have not already been
run against the current database, so in this case you will just see:
@@ -875,12 +1174,16 @@ Rails is smart enough to only execute the migrations that have not already been
h4. Associating Models
Active Record associations let you easily declare the relationship between two models. In the case of comments and posts, you could write out the relationships this way:
Active Record associations let you easily declare the relationship between two
models. In the case of comments and posts, you could write out the relationships
this way:
* Each comment belongs to one post
* One post can have many comments
In fact, this is very close to the syntax that Rails uses to declare this association. You've already seen the line of code inside the Comment model that makes each comment belong to a Post:
In fact, this is very close to the syntax that Rails uses to declare this
association. You've already seen the line of code inside the Comment model that
makes each comment belong to a Post:
<ruby>
class Comment <ActiveRecord::Base
...
...
@@ -900,13 +1203,20 @@ class Post < ActiveRecord::Base
end
</ruby>
These two declarations enable a good bit of automatic behavior. For example, if you have an instance variable +@post+ containing a post, you can retrieve all the comments belonging to that post as the array +@post.comments+.
These two declarations enable a good bit of automatic behavior. For example, if
you have an instance variable +@post+ containing a post, you can retrieve all
the comments belonging to that post as the array +@post.comments+.
TIP: For more information on Active Record associations, see the "Active Record Associations":association_basics.html guide.
TIP: For more information on Active Record associations, see the "Active Record
Associations":association_basics.html guide.
h4. Adding a Route for Comments
As with the +home+ controller, we will need to add a route so that Rails knows where we would like to navigate to see +comments+. Open up the +config/routes.rb+ file again, you will see an entry that was added automatically for +posts+ near the top by the scaffold generator, +resources :posts+, edit it as follows:
As with the +home+ controller, we will need to add a route so that Rails knows
where we would like to navigate to see +comments+. Open up the
+config/routes.rb+ file again, you will see an entry that was added
automatically for +posts+ near the top by the scaffold generator, +resources
:posts+, edit it as follows:
<ruby>
resources :posts do
...
...
@@ -914,13 +1224,17 @@ resources :posts do
end
</ruby>
This creates +comments+ as a _nested resource_ within +posts+. This is another part of capturing the hierarchical relationship that exists between posts and comments.
This creates +comments+ as a _nested resource_ within +posts+. This is another
part of capturing the hierarchical relationship that exists between posts and
comments.
TIP: For more information on routing, see the "Rails Routing from the Outside In":routing.html guide.
TIP: For more information on routing, see the "Rails Routing from the Outside
In":routing.html guide.
h4. Generating a Controller
With the model in hand, you can turn your attention to creating a matching controller. Again, there's a generator for this:
With the model in hand, you can turn your attention to creating a matching
controller. Again, there's a generator for this:
<shell>
$ rails generate controller Comments
...
...
@@ -936,9 +1250,14 @@ This creates six files and one empty directory:
* +app/assets/stylesheets/comment.css.scss+ - Cascading style sheet for the controller
* +app/assets/javascripts/comment.js.coffee+ - CoffeeScript for the controller
Like with any blog, our readers will create their comments directly after reading the post, and once they have added their comment, will be sent back to the post show page to see their comment now listed. Due to this, our +CommentsController+ is there to provide a method to create comments and delete SPAM comments when they arrive.
Like with any blog, our readers will create their comments directly after
reading the post, and once they have added their comment, will be sent back to
the post show page to see their comment now listed. Due to this, our
+CommentsController+ is there to provide a method to create comments and delete
SPAM comments when they arrive.
So first, we'll wire up the Post show template (+/app/views/posts/show.html.erb+) to let us make a new comment:
So first, we'll wire up the Post show template
(+/app/views/posts/show.html.erb+) to let us make a new comment:
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -977,7 +1296,8 @@ So first, we'll wire up the Post show template (+/app/views/posts/show.html.erb+
<%=link_to'BacktoPosts',posts_path%> |
</erb>
This adds a form on the Post show page that creates a new comment, which will call the +CommentsController+ +create+ action, so let's wire that up:
This adds a form on the Post show page that creates a new comment, which will
call the +CommentsController+ +create+ action, so let's wire that up:
<ruby>
class CommentsController <ApplicationController
...
...
@@ -989,11 +1309,21 @@ class CommentsController < ApplicationController
end
</ruby>
You'll see a bit more complexity here than you did in the controller for posts. That's a side-effect of the nesting that you've set up; each request for a comment has to keep track of the post to which the comment is attached, thus the initial find action to the Post model to get the post in question.
You'll see a bit more complexity here than you did in the controller for posts.
That's a side-effect of the nesting that you've set up; each request for a
comment has to keep track of the post to which the comment is attached, thus the
initial find action to the Post model to get the post in question.
In addition, the code takes advantage of some of the methods available for an association. We use the +create+ method on +@post.comments+ to create and save the comment. This will automatically link the comment so that it belongs to that particular post.
In addition, the code takes advantage of some of the methods available for an
association. We use the +create+ method on +@post.comments+ to create and save
the comment. This will automatically link the comment so that it belongs to that
particular post.
Once we have made the new comment, we send the user back to the original post using the +post_path(@post)+ helper. As we have already seen, this calls the +show+ action of the +PostsController+ which in turn renders the +show.html.erb+ template. This is where we want the comment to show, so let's add that to the +app/views/posts/show.html.erb+.
Once we have made the new comment, we send the user back to the original post
using the +post_path(@post)+ helper. As we have already seen, this calls the
+show+ action of the +PostsController+ which in turn renders the +show.html.erb+
template. This is where we want the comment to show, so let's add that to the
+app/views/posts/show.html.erb+.
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -1047,15 +1377,20 @@ Once we have made the new comment, we send the user back to the original post us
<%=link_to'BacktoPosts',posts_path%> |
</erb>
Now you can add posts and comments to your blog and have them show up in the right places.
Now you can add posts and comments to your blog and have them show up in the
right places.
h3. Refactoring
Now that we have Posts and Comments working, if we take a look at the +app/views/posts/show.html.erb+ template, it's getting long and awkward. We can use partials to clean this up.
Now that we have Posts and Comments working, if we take a look at the
+app/views/posts/show.html.erb+ template, it's getting long and awkward. We can
use partials to clean this up.
h4. Rendering Partial Collections
First we will make a comment partial to extract showing all the comments for the post. Create the file +app/views/comments/_comment.html.erb+ and put the following into it:
First we will make a comment partial to extract showing all the comments for the
post. Create the file +app/views/comments/_comment.html.erb+ and put the
following into it:
<erb>
<p>
...
...
@@ -1069,7 +1404,8 @@ First we will make a comment partial to extract showing all the comments for the
</p>
</erb>
Then in the +app/views/posts/show.html.erb+ you can change it to look like the following:
Then in the +app/views/posts/show.html.erb+ you can change it to look like the
following:
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -1113,11 +1449,16 @@ Then in the +app/views/posts/show.html.erb+ you can change it to look like the f
<%=link_to'BacktoPosts',posts_path%> |
</erb>
This will now render the partial in +app/views/comments/_comment.html.erb+ once for each comment that is in the +@post.comments+ collection. As the +render+ method iterates over the <tt>@post.comments</tt> collection, it assigns each comment to a local variable named the same as the partial, in this case +comment+ which is then available in the partial for us to show.
This will now render the partial in +app/views/comments/_comment.html.erb+ once
for each comment that is in the +@post.comments+ collection. As the +render+
method iterates over the <tt>@post.comments</tt> collection, it assigns each
comment to a local variable named the same as the partial, in this case
+comment+ which is then available in the partial for us to show.
h4. Rendering a Partial Form
Lets also move that new comment section out to it's own partial, again, you create a file +app/views/comments/_form.html.erb+ and in it you put:
Lets also move that new comment section out to it's own partial, again, you
create a file +app/views/comments/_form.html.erb+ and in it you put:
<erb>
<%=form_for([@post,@post.comments.build])do|f|%>
...
...
@@ -1167,15 +1508,22 @@ Then you make the +app/views/posts/show.html.erb+ look like the following:
<%=link_to'BacktoPosts',posts_path%> |
</erb>
The second render just defines the partial template we want to render, <tt>comments/form</tt>, Rails is smart enough to spot the forward slash in that string and realize that you want to render the <tt>_form.html.erb</tt> file in the <tt>app/views/comments</tt> directory.
The second render just defines the partial template we want to render,
<tt>comments/form</tt>, Rails is smart enough to spot the forward slash in that
string and realize that you want to render the <tt>_form.html.erb</tt> file in
the <tt>app/views/comments</tt> directory.
The +@post+ object is available to any partials rendered in the view because we defined it as an instance variable.
The +@post+ object is available to any partials rendered in the view because we
defined it as an instance variable.
h3. Deleting Comments
Another important feature on a blog is being able to delete SPAM comments. To do this, we need to implement a link of some sort in the view and a +DELETE+ action in the +CommentsController+.
Another important feature on a blog is being able to delete SPAM comments. To do
this, we need to implement a link of some sort in the view and a +DELETE+ action
in the +CommentsController+.
So first, let's add the delete link in the +app/views/comments/_comment.html.erb+ partial:
So first, let's add the delete link in the
+app/views/comments/_comment.html.erb+ partial:
<erb>
<p>
...
...
@@ -1195,7 +1543,10 @@ So first, let's add the delete link in the +app/views/comments/_comment.html.erb
</p>
</erb>
Clicking this new "Destroy Comment" link will fire off a <tt>DELETE /posts/:id/comments/:id</tt> to our +CommentsController+, which can then use this to find the comment we want to delete, so let's add a destroy action to our controller:
Clicking this new "Destroy Comment" link will fire off a <tt>DELETE
/posts/:id/comments/:id</tt> to our +CommentsController+, which can then use
this to find the comment we want to delete, so let's add a destroy action to our
controller:
<ruby>
class CommentsController <ApplicationController
...
...
@@ -1216,12 +1567,17 @@ class CommentsController < ApplicationController
end
</ruby>
The +destroy+ action will find the post we are looking at, locate the comment within the <tt>@post.comments</tt> collection, and then remove it from the database and send us back to the show action for the post.
The +destroy+ action will find the post we are looking at, locate the comment
within the <tt>@post.comments</tt> collection, and then remove it from the
database and send us back to the show action for the post.
h4. Deleting Associated Objects
If you delete a post then its associated comments will also need to be deleted. Otherwise they would simply occupy space in the database. Rails allows you to use the +dependent+ option of an association to achieve this. Modify the Post model, +app/models/post.rb+, as follows:
If you delete a post then its associated comments will also need to be deleted.
Otherwise they would simply occupy space in the database. Rails allows you to
use the +dependent+ option of an association to achieve this. Modify the Post
model, +app/models/post.rb+, as follows:
<ruby>
class Post <ActiveRecord::Base
...
...
@@ -1234,13 +1590,20 @@ end
h3. Security
If you were to publish your blog online, anybody would be able to add, edit and delete posts or delete comments.
If you were to publish your blog online, anybody would be able to add, edit and
delete posts or delete comments.
Rails provides a very simple HTTP authentication system that will work nicely in this situation.
Rails provides a very simple HTTP authentication system that will work nicely in
this situation.
In the +PostsController+ we need to have a way to block access to the various actions if the person is not authenticated, here we can use the Rails <tt>http_basic_authenticate_with</tt> method, allowing access to the requested action if that method allows it.
In the +PostsController+ we need to have a way to block access to the various
actions if the person is not authenticated, here we can use the Rails
<tt>http_basic_authenticate_with</tt> method, allowing access to the requested
action if that method allows it.
To use the authentication system, we specify it at the top of our +PostsController+, in this case, we want the user to be authenticated on every action, except for +index+ and +show+, so we write that:
To use the authentication system, we specify it at the top of our
+PostsController+, in this case, we want the user to be authenticated on every
action, except for +index+ and +show+, so we write that:
<ruby>
class PostsController <ApplicationController
...
...
@@ -1255,7 +1618,8 @@ class PostsController < ApplicationController
#snippedforbrevity
</ruby>
We also only want to allow authenticated users to delete comments, so in the +CommentsController+ we write:
We also only want to allow authenticated users to delete comments, so in the
+CommentsController+ we write:
<ruby>
class CommentsController <ApplicationController
...
...
@@ -1267,16 +1631,21 @@ class CommentsController < ApplicationController
#snippedforbrevity
</ruby>
Now if you try to create a new post, you will be greeted with a basic HTTP Authentication challenge
Now if you try to create a new post, you will be greeted with a basic HTTP
Another feature of your average blog is the ability to tag posts. To implement this feature your application needs to interact with more than one model on a single form. Rails offers support for nested forms.
Another feature of your average blog is the ability to tag posts. To implement
this feature your application needs to interact with more than one model on a
single form. Rails offers support for nested forms.
To demonstrate this, we will add support for giving each post multiple tags, right in the form where you create the post. First, create a new model to hold the tags:
To demonstrate this, we will add support for giving each post multiple tags,
right in the form where you create the post. First, create a new model to hold
the tags:
<shell>
$ rails generate model tag name:string post:references
...
...
@@ -1288,7 +1657,9 @@ Again, run the migration to create the database table:
$ rake db:migrate
</shell>
Next, edit the +post.rb+ file to create the other side of the association, and to tell Rails (via the +accepts_nested_attributes_for+ macro) that you intend to edit tags via posts:
Next, edit the +post.rb+ file to create the other side of the association, and
to tell Rails (via the +accepts_nested_attributes_for+ macro) that you intend to
edit tags via posts:
<ruby>
class Post <ActiveRecord::Base
...
...
@@ -1304,7 +1675,10 @@ class Post < ActiveRecord::Base
end
</ruby>
The +:allow_destroy+ option on the nested attribute declaration tells Rails to display a "remove" checkbox on the view that you'll build shortly. The +:reject_if+ option prevents saving new tags that do not have any attributes filled in.
The +:allow_destroy+ option on the nested attribute declaration tells Rails to
display a "remove" checkbox on the view that you'll build shortly. The
+:reject_if+ option prevents saving new tags that do not have any attributes
filled in.
We will modify +views/posts/_form.html.erb+ to render a partial to make a tag:
...
...
@@ -1343,13 +1717,20 @@ We will modify +views/posts/_form.html.erb+ to render a partial to make a tag:
<%end%>
</erb>
Note that we have changed the +f+ in +form_for(@post) do |f|+ to +post_form+ to make it easier to understand what is going on.
Note that we have changed the +f+ in +form_for(@post) do |f|+ to +post_form+ to
make it easier to understand what is going on.
This example shows another option of the render helper, being able to pass in local variables, in this case, we want the local variable +form+ in the partial to refer to the +post_form+ object.
This example shows another option of the render helper, being able to pass in
local variables, in this case, we want the local variable +form+ in the partial
to refer to the +post_form+ object.
We also add a <tt>@post.tags.build</tt> at the top of this form, this is to make sure there is a new tag ready to have it's name filled in by the user. If you do not build the new tag, then the form will not appear as there is no new Tag object ready to create.
We also add a <tt>@post.tags.build</tt> at the top of this form, this is to make
sure there is a new tag ready to have it's name filled in by the user. If you do
not build the new tag, then the form will not appear as there is no new Tag
object ready to create.
Now create the folder <tt>app/views/tags</tt> and make a file in there called <tt>_form.html.erb</tt> which contains the form for the tag:
Now create the folder <tt>app/views/tags</tt> and make a file in there called
<tt>_form.html.erb</tt> which contains the form for the tag:
<erb>
<%=form.fields_for:tagsdo|tag_form|%>
...
...
@@ -1366,7 +1747,8 @@ Now create the folder <tt>app/views/tags</tt> and make a file in there called <t
<%end%>
</erb>
Finally, we will edit the <tt>app/views/posts/show.html.erb</tt> template to show our tags.
Finally, we will edit the <tt>app/views/posts/show.html.erb</tt> template to
show our tags.
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -1402,13 +1784,18 @@ Finally, we will edit the <tt>app/views/posts/show.html.erb</tt> template to sho
<%=link_to'BacktoPosts',posts_path%> |
</erb>
With these changes in place, you'll find that you can edit a post and its tags directly on the same view.
With these changes in place, you'll find that you can edit a post and its tags
directly on the same view.
However, that method call <tt>@post.tags.map { |t| t.name }.join(", ")</tt> is awkward, we could handle this by making a helper method.
However, that method call <tt>@post.tags.map { |t| t.name }.join(", ")</tt> is
awkward, we could handle this by making a helper method.
h3. View Helpers
View Helpers live in <tt>app/helpers</tt> and provide small snippets of reusable code for views. In our case, we want a method that strings a bunch of objects together using their name attribute and joining them with a comma. As this is for the Post show template, we put it in the PostsHelper.
View Helpers live in <tt>app/helpers</tt> and provide small snippets of reusable
code for views. In our case, we want a method that strings a bunch of objects
together using their name attribute and joining them with a comma. As this is
for the Post show template, we put it in the PostsHelper.
Open up <tt>app/helpers/posts_helper.rb</tt> and add the following:
...
...
@@ -1420,7 +1807,8 @@ module PostsHelper
end
</erb>
Now you can edit the view in <tt>app/views/posts/show.html.erb</tt> to look like this:
Now you can edit the view in <tt>app/views/posts/show.html.erb</tt> to look like
this:
<erb>
<pclass="notice"><%=notice%></p>
...
...
@@ -1458,7 +1846,10 @@ Now you can edit the view in <tt>app/views/posts/show.html.erb</tt> to look like
h3. What's Next?
Now that you've seen your first Rails application, you should feel free to update it and experiment on your own. But you don't have to do everything without help. As you need assistance getting up and running with Rails, feel free to consult these support resources:
Now that you've seen your first Rails application, you should feel free to
update it and experiment on your own. But you don't have to do everything
without help. As you need assistance getting up and running with Rails, feel
free to consult these support resources:
* The "Ruby on Rails guides":index.html
* The "Ruby on Rails Tutorial":http://railstutorial.org/book
...
...
@@ -1473,9 +1864,18 @@ Rails also comes with built-in help that you can generate using the rake command
h3. Configuration Gotchas
The easiest way to work with Rails is to store all external data as UTF-8. If you don't, Ruby libraries and Rails will often be able to convert your native data into UTF-8, but this doesn't always work reliably, so you're better off ensuring that all external data is UTF-8.
If you have made a mistake in this area, the most common symptom is a black diamond with a question mark inside appearing in the browser. Another common symptom is characters like "ü" appearing instead of "ü". Rails takes a number of internal steps to mitigate common causes of these problems that can be automatically detected and corrected. However, if you have external data that is not stored as UTF-8, it can occasionally result in these kinds of issues that cannot be automatically detected by Rails and corrected.
The easiest way to work with Rails is to store all external data as UTF-8. If
you don't, Ruby libraries and Rails will often be able to convert your native
data into UTF-8, but this doesn't always work reliably, so you're better off
ensuring that all external data is UTF-8.
If you have made a mistake in this area, the most common symptom is a black
diamond with a question mark inside appearing in the browser. Another common
symptom is characters like "ü" appearing instead of "ü". Rails takes a number
of internal steps to mitigate common causes of these problems that can be
automatically detected and corrected. However, if you have external data that is
not stored as UTF-8, it can occasionally result in these kinds of issues that
cannot be automatically detected by Rails and corrected.
Two very common sources of data that are not UTF-8:
* Your text editor: Most text editors (such as Textmate), default to saving files as
@@ -477,7 +477,7 @@ Several methods are provided that allow you to control all this:
For example, this migration
<ruby>
<pre>
class CreateProducts < ActiveRecord::Migration
def change
suppress_messages do
...
...
@@ -496,7 +496,7 @@ class CreateProducts < ActiveRecord::Migration
end
end
end
</ruby>
</pre>
generates the following output
...
...
@@ -514,40 +514,107 @@ If you just want Active Record to shut up then running +rake db:migrate VERBOSE=
h3. Using Models in Your Migrations
When creating or updating data in a migration it is often tempting to use one of your models. After all they exist to provide easy access to the underlying data. This can be done but some caution should be observed.
When creating or updating data in a migration it is often tempting to use one of your models. After all they exist to provide easy access to the underlying data. This can be done, but some caution should be observed.
Consider for example a migration that uses the +Product+ model to update a row in the corresponding table. Alice later updates the +Product+ model, adding a new column and a validation on it. Bob comes back from holiday, updates the source and runs outstanding migrations with +rake db:migrate+, including the one that used the +Product+ model. When the migration runs the source is up to date and so the +Product+ model has the validation added by Alice. The database however is still old and so does not have that column and an error ensues because that validation is on a column that does not yet exist.
For example, problems occur when the model uses database columns which are (1) not currently in the database and (2) will be created by this or a subsequent migration.
Frequently I just want to update rows in the database without writing out the SQL by hand: I'm not using anything specific to the model. One pattern for this is to define a copy of the model inside the migration itself, for example:
Consider this example, where Alice and Bob are working on the same code base which contains a +Product+ model:
<ruby>
class AddPartNumberToProducts < ActiveRecord::Migration
class Product < ActiveRecord::Base
Bob goes on vacation.
Alice creates a migration for the +products+ table which adds a new column and initializes it.
She also adds a validation to the Product model for the new column.
Alice adds a second migration which adds and initializes another column to the +products+ table and also adds a validation to the Product model for the new column.
The migration has its own minimal copy of the +Product+ model and no longer cares about the +Product+ model defined in the application.
</pre>
h4. Dealing with Changing Models
<pre>
# app/model/product.rb
For performance reasons information about the columns a model has is cached. For example if you add a column to a table and then try and use the corresponding model to insert a new row it may try to use the old column information. You can force Active Record to re-read the column information with the +reset_column_information+ method, for example
class Product < ActiveRecord::Base
validates_presence_of :flag
validates_presence_of :fuzz
end
</pre>
<ruby>
class AddPartNumberToProducts < ActiveRecord::Migration
Both migrations work for Alice.
Bob comes back from vacation and:
# updates the source - which contains both migrations and the latests version of the Product model.
# runs outstanding migrations with +rake db:migrate+, which includes the one that updates the +Product+ model.
The migration crashes because when the model attempts to save, it tries to validate the second added column, which is not in the database when the _first_ migration runs.
<pre>
rake aborted!
An error has occurred, this and all later migrations canceled:
undefined method `fuzz' for #<Product:0x000001049b14a0>
</pre>
A fix for this is to create a local model within the migration. This keeps rails from running the validations, so that the migrations run to completion.
When using a faux model, it's a good idea to call +Product.reset_column_information+ to refresh the ActiveRecord cache for the Product model prior to updating data in the database.
If Alice had done this instead, there would have been no problem:
