Make exists? use bound values.

When we build a query with an inline value that is a numeric (e.g.
because it's out of range for an int4) PostgreSQL doesn't use an index
on the column, since it's now comparing numerics and not int4s.

This leads to a _very_ slow query.

When we use bound parameters instead of inline values PostgreSQL
raises numeric_value_out_of_range since no automatic coercion happens.

activerecord/lib/active_record/relation/finder_methods.rb

@@ -292,7 +292,12 @@ def exists?(conditions = :none)
       when Array, Hash
         relation = relation.where(conditions)
       else
-        relation = relation.where(table[primary_key].eq(conditions)) if conditions != :none
+        if conditions != :none
+          column = columns_hash[primary_key]
+          substitute = connection.substitute_at(column, bind_values.length)
+          relation = where(table[primary_key].eq(substitute))
+          relation.bind_values += [[column, conditions]]
+        end
       end
 
       connection.select_value(relation, "#{name} Exists", relation.bind_values) ? true : false

activerecord/test/cases/finder_test.rb

@@ -58,15 +58,27 @@ def test_exists
     assert_equal false, Topic.exists?(45)
     assert_equal false, Topic.exists?(Topic.new)
 
+    assert_raise(NoMethodError) { Topic.exists?([1,2]) }
+  end
+
+  def test_exists_fails_when_parameter_has_invalid_type
+    begin
+      assert_equal false, Topic.exists?(("9"*53).to_i) # number that's bigger than int
+      flunk if defined? ActiveRecord::ConnectionAdapters::PostgreSQLAdapter and Topic.connection.is_a? ActiveRecord::ConnectionAdapters::PostgreSQLAdapter # PostgreSQL does raise here
+    rescue ActiveRecord::StatementInvalid
+      # PostgreSQL complains that it can't coerce a numeric that's bigger than int into int
+    rescue Exception
+      flunk
+    end
+
     begin
       assert_equal false, Topic.exists?("foo")
+      flunk if defined? ActiveRecord::ConnectionAdapters::PostgreSQLAdapter and Topic.connection.is_a? ActiveRecord::ConnectionAdapters::PostgreSQLAdapter # PostgreSQL does raise here
     rescue ActiveRecord::StatementInvalid
       # PostgreSQL complains about string comparison with integer field
     rescue Exception
       flunk
     end
-
-    assert_raise(NoMethodError) { Topic.exists?([1,2]) }
   end
 
   def test_exists_does_not_select_columns_without_alias