Undefined method in ActiveSupport concern

Question

I have a model that extends ActiveRecord::Base and includes a concern:

class User < ActiveRecord::Base
    include UserConcern

    def self.create_user()
        ...
        results = some_method()
    end

end

UserConcern is stored in the concerns directory:

module UserConcern
    extend ActiveSupport::Concern

    def some_method()
        ...
    end
end

I am getting a run-time error when I try to create a new user by calling the create_user method that looks like this:

undefined method 'some_method' for #<Class:0x000000...>

I have two questions about this:

Why is the some_method undefined? It seems to me that I am properly including it with the statement include UserConcern. Does it have something to do with my User class extending ActiveRecord::Base? Or maybe something to do with the fact that I am calling some_methods() from a class method (i.e. self.create_user())?
Why does the run-time error refer to #<Class:0x000000...> instead of to #<User:0x000000...>?

Indeed the error is because you are trying to call an instance method inside a class method. And the runtime error refers to #<Class because the class User is an instance of the class Class. — nbermudezs
Either your some_method depends on an instance or not, if it doesn't make it a class method and everything should work as you expect. If it does, then you need to rethink why you are calling it inside a class method. Maybe you expect an instance as an argument? — nbermudezs
And finally, if in fact your method create_user does what it name indicates then you probably take a look at the before and after create callbacks to do something when a new instance is created. — nbermudezs

yhirano55 yhirano55 · Accepted Answer · 2016-01-17T00:13:25

try it

models/concerns/user_concern.rb:

module UserConcern
  extend ActiveSupport::Concern

  def some_instance_method
    'some_instance_method'
  end

  included do
    def self.some_class_method
      'some_class_method'
    end
  end
end

models/user.rb:

class User < ActiveRecord::Base
  include UserConcern
  def self.create_user
    self.some_class_method
  end
end

rails console:

user = User.new
user.some_instance_method
# => "some_instance_method"

User.some_class_method
# => "some_class_method"

User.create_user
# => "some_class_method"

http://api.rubyonrails.org/classes/ActiveSupport/Concern.html

Undefined method in ActiveSupport concern

1 Answers