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.

1 files changed, 16 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6494c7374e..1ade4f8751 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,19 @@
+*   Change `ActiveRecord::Relation#update` behavior so that it can
+    be called without passing ids of the records to be updated.
+
+    This change allows to update multiple records returned by
+    `ActiveRecord::Relation` with callbacks and validations.
+
+        # Before
+        # ArgumentError: wrong number of arguments (1 for 2)
+        Comment.where(group: 'expert').update(body: "Group of Rails Experts")
+
+        # After
+        # Comments with group expert updated with body "Group of Rails Experts"
+        Comment.where(group: 'expert').update(body: "Group of Rails Experts")
+
+    *Prathamesh Sonpatki*
+
 *   Introduce `force: :cascade` option for `create_table`. Using this option
     will recreate tables even if they have dependent objects (like foreign keys).
     `db/schema.rb` now uses `force: :cascade`. This makes it possible to