Run SQL only if attribute changed for update_attribute method

 - This is based on https://github.com/rails/rails/issues/18400 but
   tackling same issue with update_attribute method instead of update method.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/persistence_test.rb b/activerecord/test/cases/persistence_test.rb
index d6816041bc..2803ad2de0 100644
--- a/activerecord/test/cases/persistence_test.rb
+++ b/activerecord/test/cases/persistence_test.rb
@@ -356,6 +356,16 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_equal("David", topic_reloaded.author_name)
   end
 
+  def test_update_attribute_does_not_run_sql_if_attribute_is_not_changed
+    klass = Class.new(Topic) do
+      def self.name; 'Topic'; end
+    end
+    topic = klass.create(title: 'Another New Topic')
+    assert_queries(0) do
+      topic.update_attribute(:title, 'Another New Topic')
+    end
+  end
+
   def test_delete
     topic = Topic.find(1)
     assert_equal topic, topic.delete, 'topic.delete did not return self'