Question

I have a model named Promotion.

class Promotion < ActiveRecord::Base; 
  FORMATS = [0,1]
end

I also have another subclass named ‘Promotion’ defined in a file in the /lib folder of my app.

module Faker
  module MyProject
    module Promotion
      def format
        # Need to access Promotion::FORMATS
      end
    end
  end
end

I need to reference a constant defined in the AR class from within the other module. The only way I’ve been able to do it so far is to use

ActiveRecord::Base.descendants.detect{|model| model.name == 'Promotion'}::FORMATS

I’m wondering if there is a better way to go about this?

CORRECTION

Turns out that only worked from the command line. When I applied it to the Promotion submodule, it didn’t return the same list of models. So rather than a better way, what is the way to access an AR model in a non-ambiguous way? I’ve updated the definitions above to better illustrate what I’m trying to do.

Answer 1

This is a question of how constants are scoped.

The simple answer is

::Promotion

In your example

class Promotion < ActiveRecord::Base; end

Promotion has been defined on the global scope so can be accessed in 3 ways

• Promotion
• ::Promotion
• Object::Promotion

But within your module Faker::MyProject any reference to Promotion will look up this namespace

If Faker::MyProject::Promotion exists it’ll return this.

I suggest you make a habit of refering to ::Promotion in these type of cases.

Example:

class A; end
module B; class A; end

A         #=> A
::A       #=> A
Object::A #=> A

B.module_eval("A")   #=> B::A
B.module_eval("::A") #=> A