Revert "Remove update_attribute."

This reverts commit a7f4b0a1231bf3c65db2ad4066da78c3da5ffb01.

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

2 files changed, 20 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 703265c334..c1d57855a9 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/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
   #     ...
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 6b4b9bd103..c64e3e6ccf 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/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.