Rails: dynamically define class method based on parent class name within module/concern

Question

I want to dynamically generate a class method in a Mixin, based on the class name that include this Mixin.

Here is my current code:

module MyModule  
  extend ActiveSupport::Concern  

  # def some_methods  
  #   ...  
  # end  

  module ClassMethods  

    # Here is where I'm stuck...
    define_method "#{self.name.downcase}_status" do  
      # do something...  
    end  

  end  
end  

class MyClass < ActiveRecord::Base  
  include MyModule  
end  

# What I'm trying to achieve:
MyClass.myclass_status

But this give me the following method name:

MyClass.mymodule::classmethods_status

Getting the base class name inside the method definition works (self, self.name...) but I can't make it works for the method name...

So far, I've tried

define_method "#{self}"
define_method "#{self.name"
define_method "#{self.class}"
define_method "#{self.class.name}"
define_method "#{self.model_name}"
define_method "#{self.parent.name}"

But none of this seems to do the trick :/

Is there any way I can retrieve the base class name (not sure what to call the class that include my module). I've been struggling with this problem for hours now and I can't seem to figure out a clean solution :(

Thanks!

cl3m · Accepted Answer · 2013-02-05 14:29:19Z

9

I found a clean solution: using define_singleton_method (available in ruby v1.9.3)

module MyModule  
  extend ActiveSupport::Concern  

  included do
    define_singleton_method "#{self.name}_status" do
      # do stuff
    end
  end

  # def some_methods  
  #   ...  
  # end  

  module ClassMethods  
    # Not needed anymore!
  end  
end

answered Feb 5, 2013 at 14:29

cl3m

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Comments

Frederick Cheung · Accepted Answer · 2013-02-05 12:26:55Z

7

You can't do it like that - at this point it is not yet known which class (or classes) are including the module.

If you define a self.included method it will be called each time the module is included and the thing doing the including will be passed as an argument. Alternatively since you are using AS::Concern you can do

included do 
  #code here is executed in the context of the including class
end

answered Feb 5, 2013 at 12:26

Frederick Cheung

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1 Comment

cl3m Over a year ago

Thanks for the explanation. I used define_singleton_method inside the included do #... end block: define_singleton_method "#{self.name}_status" do #... end `

Kaeros · Accepted Answer · 2013-02-05 12:28:48Z

1

You can do something like this:

module MyModule
  def self.included(base)
    (class << base; self; end).send(:define_method, "#{base.name.downcase}_status") do
      puts "Hey!"
  end

  base.extend(ClassMethods)
end

  module ClassMethods
    def other_method
      puts "Hi!"
    end
  end
end

class MyClass
  include MyModule
end

MyClass.myclass_status
MyClass.other_method

answered Feb 5, 2013 at 12:28

Kaeros

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Comments

Yevgeniy Anfilofyev · Accepted Answer · 2013-02-05 12:38:57Z

1

Works for extend:

module MyModule  
  def self.extended who
    define_method "#{who.name.downcase}_status" do
      p "Inside"
    end
  end
end  

class MyClass  
  extend MyModule  
end  

MyClass.myclass_status

answered Feb 5, 2013 at 12:38

Yevgeniy Anfilofyev

4,85728 silver badges27 bronze badges

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