Understanding the MVC pattern is key to understanding Rails. MVC divides your
application into three layers: Model, View, and Controller, each with a specific responsibility.
The _Model layer_ represents the domain model (such as Account, Product,
## Model layer
The _**Model layer**_ represents the domain model (such as Account, Product,
Person, Post, etc.) and encapsulates the business logic specific to
your application. In Rails, database-backed model classes are derived from
`ActiveRecord::Base`. Active Record allows you to present the data from
`ActiveRecord::Base`. [Active Record](activerecord/README.rdoc) allows you to present the data from
database rows as objects and embellish these data objects with business logic
methods. You can read more about Active Record in its [README](activerecord/README.rdoc).
methods.
Although most Rails models are backed by a database, models can also be ordinary
Ruby classes, or Ruby classes that implement a set of interfaces as provided by
the Active Model module. You can read more about Active Model in its [README](activemodel/README.rdoc).
the [Active Model](activemodel/README.rdoc) module.
## Controller layer
The _Controller layer_ is responsible for handling incoming HTTP requests and
The _**Controller layer**_ is responsible for handling incoming HTTP requests and
providing a suitable response. Usually this means returning HTML, but Rails controllers
can also generate XML, JSON, PDFs, mobile-specific views, and more. Controllers load and
manipulate models, and render view templates in order to generate the appropriate HTTP response.
In Rails, incoming requests are routed by Action Dispatch to an appropriate controller, and
controller classes are derived from `ActionController::Base`. Action Dispatch and Action Controller
are bundled together in Action Pack. You can read more about Action Pack in its
[README](actionpack/README.rdoc).
are bundled together in [Action Pack](actionpack/README.rdoc).
The _View layer_ is composed of "templates" that are responsible for providing
## View layer
The _**View layer**_ is composed of "templates" that are responsible for providing
appropriate representations of your application's resources. Templates can
come in a variety of formats, but most view templates are HTML with embedded
Ruby code (ERB files). Views are typically rendered to generate a controller response,
or to generate the body of an email. In Rails, View generation is handled by Action View.
You can read more about Action View in its [README](actionview/README.rdoc).
or to generate the body of an email. In Rails, View generation is handled by [Action View](actionview/README.rdoc).
## Frameworks and libraries
Active Record, Active Model, Action Pack, and Action View can each be used independently outside Rails.
In addition to that, Rails also comes with Action Mailer ([README](actionmailer/README.rdoc)), a library
to generate and send emails; Active Job ([README](activejob/README.md)), a
[Active Record](activerecord/README.rdoc), [Active Model](activemodel/README.rdoc), [Action Pack](actionpack/README.rdoc), and [Action View](actionview/README.rdoc) can each be used independently outside Rails.
In addition to that, Rails also comes with [Action Mailer](actionmailer/README.rdoc), a library
to generate and send emails; [Active Job](activejob/README.md), a
framework for declaring jobs and making them run on a variety of queueing
backends; Action Cable ([README](actioncable/README.md)), a framework to
integrate WebSockets with a Rails application;
Active Storage ([README](activestorage/README.md)), a library to attach cloud
backends; [Action Cable](actioncable/README.md), a framework to
integrate WebSockets with a Rails application; [Active Storage](activestorage/README.md), a library to attach cloud
and local files to Rails applications;
and Active Support ([README](activesupport/README.rdoc)), a collection
and [Active Support](activesupport/README.rdoc), a collection
of utility classes and standard library extensions that are useful for Rails,
