Accessing model attributes from module method

Question

I know there are some gems out there that give you slugs out of the box. However, I think doing something similar is a good way of learning.

Since I'm using slugs in several models, I decided to create a module and include it via ActiveSupport::Concern.

This is my module sluggable.rb:

module Sluggable
    extend ActiveSupport::Concern

    module ClassMethods
        def slug(*atts_to_slug)
            after_validation set_slug(atts_to_slug)
        end

        def set_slug(atts)
            slug_string = atts.map{|f| f.parameterize}.join("-")
            # Then I would think I can do something like:
            # model_instance.send("slug", slug_string)
        end
    end
end

Then I'd like to do something like this in the model:

class Classification < ApplicationRecord
    include Sluggable

    slug :name, :street
end

The problem I'm finding is:

How do I set the model's attribute slug from the module?

Siim Liiser · Accepted Answer · 2020-10-23 10:19:41Z

after_validation is a callback that expects a method name, block or a callable object (proc/lambda).

The way you're currently using it. It will call set_slug once when slug is first called and not after that.

slug should set the required attributes into some (class-level) variable. after_validation should call the set_slug method that should be an instance method. Then in the set_slug instance method you have access to all the attributes.

module Sluggable
  extend ActiveSupport::Concern

  module ClassMethods
    def slug(*atts_to_slug)
      @atts_to_slug = atts_to_slug
    end

    def atts_to_slug
      @atts_to_slug
    end
  end

  included do # instance scope
    after_validation :set_slug

    def set_slug
      slug_string = self.class.atts_to_slug.map do |f|
        # send since we're in the instance and I want to just call `name`
        public_send(f).parameterize
      end.join("-")
      self.slug = slug_string
    end
  end
end

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