Allow ActiveRecord::Relation#update to run on result of a relation with callbacks and validations

- Right now, there is no method to update multiple records with
  validations and callbacks.
- Changed the behavior of existing `update` method so that when `id`
  attribute is not given and the method is called on an `Relation`
  object, it will execute update for every record of the `Relation` and
  will run validations and callbacks for every record.
- Added test case for validating that the callbacks run when `update` is
  called on a `Relation`.
- Changed test_create_columns_not_equal_attributes test from
  persistence_test to include author_name column on topics table as it
  it used in before_update callback.
- This change introduces performance issues when a large number of
  records are to be updated because it runs UPDATE query for every
  record of the result. The `update_all` method can be used in that case
  if callbacks are not required because it will only run single UPDATE
  for all the records.

2 files changed, 22 insertions, 2 deletions

diff --git a/activerecord/test/cases/persistence_test.rb b/activerecord/test/cases/persistence_test.rb
index 6fc4731f01..67a929ba09 100644
--- a/activerecord/test/cases/persistence_test.rb
+++ b/activerecord/test/cases/persistence_test.rb
@@ -252,8 +252,10 @@ class PersistenceTest < ActiveRecord::TestCase
 
   def test_create_columns_not_equal_attributes
     topic = Topic.instantiate(
-      'title'          => 'Another New Topic',
-      'does_not_exist' => 'test'
+      'attributes' => {
+        'title'          => 'Another New Topic',
+        'does_not_exist' => 'test'
+      }
     )
     assert_nothing_raised { topic.save }
   end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 3a0398d08d..17943f5457 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -22,6 +22,11 @@ class RelationTest < ActiveRecord::TestCase
   fixtures :authors, :topics, :entrants, :developers, :companies, :developers_projects, :accounts, :categories, :categorizations, :posts, :comments,
     :tags, :taggings, :cars, :minivans
 
+  class TopicWithCallbacks < ActiveRecord::Base
+    self.table_name = :topics
+    before_update { |topic| topic.author_name = 'David' if topic.author_name.blank? }
+  end
+
   def test_do_not_double_quote_string_id
     van = Minivan.last
     assert van
@@ -1429,6 +1434,19 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal posts(:welcome),  comments(:greetings).post
   end
 
+  def test_update_on_relation
+    topic1 = TopicWithCallbacks.create! title: 'arel', author_name: nil
+    topic2 = TopicWithCallbacks.create! title: 'activerecord', author_name: nil
+    topics = TopicWithCallbacks.where(id: [topic1.id, topic2.id])
+    topics.update(title: 'adequaterecord')
+
+    assert_equal 'adequaterecord', topic1.reload.title
+    assert_equal 'adequaterecord', topic2.reload.title
+    # Testing that the before_update callbacks have run
+    assert_equal 'David', topic1.reload.author_name
+    assert_equal 'David', topic2.reload.author_name
+  end
+
   def test_distinct
     tag1 = Tag.create(:name => 'Foo')
     tag2 = Tag.create(:name => 'Foo')