Including a module in a Rails 5 Application Record class

问题

I am using Application Record to simplify shared logic throughout an application.

Here's an example that writes a scope for a boolean and its inverse. This works well:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  def self.boolean_scope(attr, opposite = nil)
    scope(attr, -> { where("#{attr}": true) })
    scope(opposite, -> { where("#{attr}": false) }) if opposite.present?
  end
end

class User < ApplicationRecord
  boolean_scope :verified, :unverified
end

class Message < ApplicationRecord
  boolean_scope :sent, :pending
end

My Application Record class got long enough it made sense for me to break it up into individual modules and load those as needed.

Here's my attempted solution:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  include ScopeHelpers
end

module ScopeHelpers
  def self.boolean_scope(attr, opposite = nil)
    scope(attr, -> { where("#{attr}": true) })
    scope(opposite, -> { where("#{attr}": false) }) if opposite.present?
  end
end

class User < ApplicationRecord
  boolean_scope :verified, :unverified
end

class Message < ApplicationRecord
  boolean_scope :sent, :pending
end

In this case, I don't get a load error, but boolean_scope is then undefined on User and Message.

Is there a way to ensure the included modules are loaded at the appropriate time and available to Application Record and its inheriting models?

---

I've also attempted to have the models include the modules directly and that did not fix the issue.

module ScopeHelpers
  def self.boolean_scope(attr, opposite = nil)
    scope(attr, -> { where("#{attr}": true) })
    scope(opposite, -> { where("#{attr}": false) }) if opposite.present?
  end
end

class User < ApplicationRecord
  include ScopeHelpers
  boolean_scope :verified, :unverified
end

class Message < ApplicationRecord
  include ScopeHelpers
  boolean_scope :sent, :pending
end

回答1:

As an alternative to @Pavan's answer, you can do this:

module ScopeHelpers
  extend ActiveSupport::Concern # to handle ClassMethods submodule

  module ClassMethods
    def boolean_scope(attr, opposite = nil)
      scope(attr, -> { where(attr => true) })
      scope(opposite, -> { where(attr => false) }) if opposite.present?
    end
  end
end

# then use it as usual
class ApplicationRecord < ActiveRecord::Base
  include ScopeHelpers
  ...
end

回答2:

In this case, I don't get a load error, but boolean_scope is then undefined on User and Message

The problem is include add methods on an instance of a class. You need to use extend

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  extend ScopeHelpers
end

Now you can call it like User.boolean_scope. Below is the example for include vs extend

module Foo
  def foo
    puts 'heyyyyoooo!'
  end
end

class Bar
  include Foo
end

Bar.new.foo # heyyyyoooo!
Bar.foo # NoMethodError: undefined method ‘foo’ for Bar:Class

class Baz
  extend Foo
end

Baz.foo # heyyyyoooo!
Baz.new.foo # NoMethodError: undefined method ‘foo’ for #<Baz:0x1e708>

回答3:

Your User and Message classes don't seem to be inheriting ApplicationRecord. How will they have access to ::boolean_scope?

Try this:

class User < ApplicationRecord
  boolean_scope :verified, :unverified
end

class Message < ApplicationRecord
  boolean_scope :sent, :pending
end

来源：https://stackoverflow.com/questions/44498962/including-a-module-in-a-rails-5-application-record-class