Concerned

Use the "concerns" pattern in any Ruby or Rails project.

Rails 3

In Gemfile:

gem 'concerned'

Usage

This gem comes with the following three helpers, that are added to Module. To require concern modules (or classes)

concerned_with
shared_concerns

And to include concern modules

include_concerns
include_shared_concerns

The concerned_with helper method expects to find a module or class matching the current namespace, fx the following will include FixtureUser::Scopes and FixtureUser::Validations into FixtureUser.

class FixtureUser
  include_concerns :scopes, :validations  
end

The include_shared_concerns expects to find a module in a shared folder somewhere in the load path that has a name of either Caching or Shared::Caching for the following example:

class FixtureUser
  include_shared_concerns :caching
end

The concerned_with and shared_concerns methods are used simply to require shared files following the namespace convention, here: project/job_matches and shared/associations.

class Project
  concerned_with :job_matches
  shared_concerns :associations
end

Concerns currently included

You can now include the Concerned module in your class or module and get acces to the meta-info: which concerns are currently included

class FixtureUser
  include Concerned
  include_concerns :scopes, :validations 
  include_shared_concerns :caching 
end

FixtureUser.my_concerns # => [:scopes, :validations]
FixtureUser.my_shared_concerns # => [:caching]
FixtureUser.all_my_shared_concerns # => [:scopes, :validations, :caching]

You can even include concerns from another scope

class FixtureUserFor
  include Concerned
  include_concerns :scopes, :validations, for: 'FixtureUser'
  include_shared_concerns :caching 
end

Will include the FixtureUser::Scopes and FixtureUser::Validations into FixtureUserFor :)

Global config

You can use the Concerned.extend_enable! to let the concern helpers also attempt to extend the host module/class with the ClassMethods module of the concerns module (if such exists). Disable it by using: Concerned.extend_disable!

Use Concerned.extend_enabled? to see if it is currently enabled or not. By default this feature is turned off.

It is usually better to use ActionSupport::Concern using extend ActiveSupport::Concern.

See fx concerns

Contributing to concerned