The initial bug which this gem fixes - rails/rails#15185 was finally fixed as rails/rails#34889

Fixed in Rails >= 6.0.3 (https://github.com/rails/rails/blob/v6.0.3/activerecord/CHANGELOG.md#rails-603-may-06-2020)

Selected virtual attributes will be now typecasted as usual attributes

#Rails version Supports rails 4.x and rails 5-5.1.4, 5.1.5, and 5.2.0.rc1 now!

Master is now runs on rails 5.2, rails_5.1.4 branch is for rails less than 5.1.5, rails_4 branch is for rails 4 support

This gem solves issue in rails: rails/rails#15185 for base_class.

It was impossible to select virtual attributes to object from its relations or any other way when using includes and where ( actually when includes becomes eager_load, i.e. when you add not SOME_CONDITION, but SOME_CONDITION_ON_INCLUDES, http://blog.bigbinary.com/2013/07/01/preload-vs-eager-load-vs-joins-vs-includes.html ).

Example from upper rails issue:

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.testval # Undefined method!

This gem solves problem for base class i.e.

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.testval # 1

but of course it doesn't include virtual attributes in included relations

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.comments.first.testval # Undefined method!

Данный gem решает проблему в рельсах с виртуальными аттрибутами при использовании includes, когда рельсы собирают в запрос в joins с алиасами на все аттрибуты. В настоящий момент в модель не собираются никаким боком виртуальные аттрибуты ( имеется ввиду когда includes ведет себя как eager_load и создает сложный одинарный запрос, подробнее: http://blog.bigbinary.com/2013/07/01/preload-vs-eager-load-vs-joins-vs-includes.html ).

В частности проблема описана здесь: rails/rails#15185

В коде примера по ссылке выше это выглядит так:

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.testval # Undefined method!

Данный gem решает эту проблему для базового класса, т.е.:

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.testval # 1

Но это не касается, объектов попадающих под инклюд:

post = Post.includes(:comments).select("posts.*, 1 as testval").where( SOME_CONDITION ).first
post.comments.first.testval # Undefined method!

Add this line to your application's Gemfile:

#rails 6
gem 'rails_select_on_includes', '~> 6.0.0'

#rails 4
gem 'rails_select_on_includes', '~> 0.4.11' 

#rails 5.1.4
gem 'rails_select_on_includes', '~> 5.1.4.0' 

#rails 5.1.5
gem 'rails_select_on_includes', '~> 5.1.5.0'


#rails 5.2
gem 'rails_select_on_includes', '~> 5.2.1'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails_select_on_includes

Works out of the box, monkey-patches base-class alias columns, for select attributes, and JoinBase with JoinDependency to proper typecasting.

It not affecting query creation, since query already contains all columns, i.e. to_sql returns same string. Works with selection in all formats:

1. 'table_name.column' or 'table_name.column as column_1' will be parsed! distinct on can be used also
2. '(subquery with AS) AS column_1 '
3. Select with aliased arel function: .select(Comment.arel_table[:id].count.as('comments_count'))
4. Select with aliased arel attirubte: .select(Comment.arel_table[:column].as('column_alias'))

Работает из коробки, нежно манки-патча алиасы прямо перед инстанцированием коллекции, а так же не менее нежно JoinBase и JoinDependency :), чтобы полученные аттрибуты были приличных типов, а не только строк, не влияет на создаваемый запрос в БД т.е to_sql не меняется.

Поддерживает select в следующих форматах :

1. 'table_name.column' or 'table_name.column as column_1' will be parsed! distinct on can be used also
2. '(subquery with AS) AS column_1 '
3. Select with aliased arel function: .select(Comment.arel_table[:id].count.as('comments_count'))
4. Select with aliased arel attirubte: .select(Comment.arel_table[:column].as('column_alias'))

rake test

Bug reports and pull requests are welcome on GitHub at https://github.com/alekseyl/rails_select_on_includes.

The gem is available as open source under the terms of the MIT License.