Move the private method #extract_schema_and_table into a separate
Utils module so that it can be tested without resorting to #send.

This caused that `find_each` was producing extra db call taking all the records from db, and was less efficient than `ActiveRecord::Base#all`.

Don't construct association scope in initializer. This yields a big performance gain for cases where the association is never used to load the target, for example with preloading. Related: #1873.

See new method mysql_creation_options. It is used by both
create_database and recreate_database so they are consistent.

(Cherry pick of 3ba3125b)

when condtions references tables from includes.
Test fail because of invalid sql:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: comments.id:
SELECT "posts".id FROM "posts" INNER JOIN "readers" ON "posts"."id" = "readers"."post_id"
WHERE "readers"."person_id" = 1 AND (comments.id is null)

Bug described in github#925

This commit will revert fix from https://github.com/rails/rails/commit/3436fdfc12d58925e3d981e0afa61084ea34736c , but tests is ok.

Bug described in #6569 ticket.

In order make Relation behavior closer to Array
Made Relation#sum to accept block and delegate it to Array#sum

In order to make CollectionAssociation behave closer to Array
Add the ability to pass block to #find method just like Array#find does.

The changes broke bulk migration tests and were fixed in 4d256bc6;
however that brought back the issue of #1857 and so this commit goes
back to the original scenario and just adds change_table to the list
of methods which are to be recorded in the CommandRecorder. The
method_missing now delegates all calls to the underlying connection as
before.

Reason: Changelogs are not to be changed in docrails.

This reverts commit 0b8cdc16.

Remove AssociationReflection#create_association and AssociationReflection#create_association! - they are not called from anywhere.

Assign the association attributes to the associated record before the before_initialize callback of the record runs. Fixes #1842.

CommandRecorder should delegate in method_missing where possible. Fixes some tests in migration_test.rb under mysql. The problem was introduced in c278a2c5.

Define to_ary on ActiveRecord::Base to return nil. Improve performance of Array#flatten under 1.9, see comment for details.

Use latest Arel syntax and pass each order by expression as separate argument to order method as otherwise invalid Oracle SQL is generated.