Revert "Remove update_attribute."

This reverts commit a7f4b0a123.

Conflicts:
	activerecord/lib/active_record/associations/has_one_association.rb
	activerecord/lib/active_record/persistence.rb
	activerecord/test/cases/base_test.rb
	activerecord/test/cases/dirty_test.rb
	activerecord/test/cases/timestamp_test.rb

activerecord/lib/active_record/migration.rb

@@ -236,7 +236,7 @@ module ActiveRecord
   #       add_column :people, :salary, :integer
   #       Person.reset_column_information
   #       Person.all.each do |p|
-  #         p.update_column :salary, SalaryCalculator.compute(p)
+  #         p.update_attribute :salary, SalaryCalculator.compute(p)
   #       end
   #     end
   #   end
@@ -256,7 +256,7 @@ module ActiveRecord
   #     ...
   #     say_with_time "Updating salaries..." do
   #       Person.all.each do |p|
-  #         p.update_column :salary, SalaryCalculator.compute(p)
+  #         p.update_attribute :salary, SalaryCalculator.compute(p)
   #       end
   #     end
   #     ...

activerecord/lib/active_record/persistence.rb

@@ -1,4 +1,3 @@
-
 module ActiveRecord
   # = Active Record Persistence
   module Persistence
@@ -166,6 +165,21 @@ module ActiveRecord
       became
     end
 
+    # Updates a single attribute and saves the record.
+    # This is especially useful for boolean flags on existing records. Also note that
+    #
+    # * Validation is skipped.
+    # * Callbacks are invoked.
+    # * updated_at/updated_on column is updated if that column is available.
+    # * Updates all the attributes that are dirty in this object.
+    #
+    def update_attribute(name, value)
+      name = name.to_s
+      verify_readonly_attribute(name)
+      send("#{name}=", value)
+      save(:validate => false)
+    end
+
     # Updates the attributes of the model from the passed-in hash and saves the
     # record, all wrapped in a transaction. If the object is invalid, the saving
     # will fail and false will be returned.
@@ -242,7 +256,7 @@ module ActiveRecord
     # Saving is not subjected to validation checks. Returns +true+ if the
     # record could be saved.
     def increment!(attribute, by = 1)
-      increment(attribute, by).update_columns(attribute => self[attribute])
+      increment(attribute, by).update_attribute(attribute, self[attribute])
     end
 
     # Initializes +attribute+ to zero if +nil+ and subtracts the value passed as +by+ (default is 1).
@@ -259,7 +273,7 @@ module ActiveRecord
     # Saving is not subjected to validation checks. Returns +true+ if the
     # record could be saved.
     def decrement!(attribute, by = 1)
-      decrement(attribute, by).update_columns(attribute => self[attribute])
+      decrement(attribute, by).update_attribute(attribute, self[attribute])
     end
 
     # Assigns to +attribute+ the boolean opposite of <tt>attribute?</tt>. So
@@ -276,7 +290,7 @@ module ActiveRecord
     # Saving is not subjected to validation checks. Returns +true+ if the
     # record could be saved.
     def toggle!(attribute)
-      toggle(attribute).update_columns(attribute => self[attribute])
+      toggle(attribute).update_attribute(attribute, self[attribute])
     end
 
     # Reloads the attributes of this object from the database.

activerecord/test/cases/dirty_test.rb

@@ -509,6 +509,16 @@ class DirtyTest < ActiveRecord::TestCase
     assert_not_nil pirate.previous_changes['updated_on'][1]
     assert !pirate.previous_changes.key?('parrot_id')
     assert !pirate.previous_changes.key?('created_on')
+
+    pirate = Pirate.find_by_catchphrase("Ahoy!")
+    pirate.update_attribute(:catchphrase, "Ninjas suck!")
+
+    assert_equal 2, pirate.previous_changes.size
+    assert_equal ["Ahoy!", "Ninjas suck!"], pirate.previous_changes['catchphrase']
+    assert_not_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+    assert !pirate.previous_changes.key?('created_on')
   end
 
   if ActiveRecord::Base.connection.supports_migrations?
@@ -534,7 +544,7 @@ class DirtyTest < ActiveRecord::TestCase
 
       pirate = target.create(:created_on => created_on)
       pirate.reload # Here mysql truncate the usec value to 0
-      
+
       pirate.created_on = created_on
       assert !pirate.created_on_changed?
     end

activerecord/test/cases/persistence_test.rb

@@ -371,10 +371,50 @@ class PersistencesTest < ActiveRecord::TestCase
     assert_raise(ActiveSupport::FrozenObjectError) { client.name = "something else" }
   end
 
+  def test_update_attribute
+    assert !Topic.find(1).approved?
+    Topic.find(1).update_attribute("approved", true)
+    assert Topic.find(1).approved?
+
+    Topic.find(1).update_attribute(:approved, false)
+    assert !Topic.find(1).approved?
+  end
+
   def test_update_attribute_does_not_choke_on_nil
     assert Topic.find(1).update_attributes(nil)
   end
 
+  def test_update_attribute_for_readonly_attribute
+    minivan = Minivan.find('m1')
+    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_attribute(:color, 'black') }
+  end
+
+  def test_update_attribute_with_one_updated
+    t = Topic.first
+    t.update_attribute(:title, 'super_title')
+    assert_equal 'super_title', t.title
+    assert !t.changed?, "topic should not have changed"
+    assert !t.title_changed?, "title should not have changed"
+    assert_nil t.title_change, 'title change should be nil'
+
+    t.reload
+    assert_equal 'super_title', t.title
+  end
+
+  def test_update_attribute_for_updated_at_on
+    developer = Developer.find(1)
+    prev_month = Time.now.prev_month
+
+    developer.update_attribute(:updated_at, prev_month)
+    assert_equal prev_month, developer.updated_at
+
+    developer.update_attribute(:salary, 80001)
+    assert_not_equal prev_month, developer.updated_at
+
+    developer.reload
+    assert_not_equal prev_month, developer.updated_at
+  end
+
   def test_update_column
     topic = Topic.find(1)
     topic.update_column("approved", true)