rails/rails — pull request #12691 by ka8725 (2013-10-29 15:00:42+00:00)
Title: Fix mistaken guide how to extend association proxy with module

There is no method `extending` for `Module`. It should be only `include` here. Tested by me both cases `exdend` and `include`. Only `include` works.

This is my code which I used to test code:

```ruby
module AssociationExtensions
module UniqMetaIds
def uniq_meta_ids
select(:meta_id).uniq.pluck(:meta_id)
end
end
end

class MetaService < ActiveRecord::Base
has_many :meta_settings do
include AssociationExtensions::UniqMetaIds
end
end

describe MetaService do
describe '#meta_settings' do
it { expect(subject.meta_settings.uniq_meta_ids).to be_blank }
end
end
```