Question

I am using Ruby on Rails 3.0.7 and I am trying to implement an act_as_article plugin for my application. What I would to do is run validation methods for the “acting as article class” inside that plugin (note: my plugin requires to create some database table columns in order to work – one of these is represented by the title attribute).

In my RoR application I have this code:

# vendor/plugins/article/lib/acts_as_article.rb
module Article
  extend ActiveSupport::Concern

  included do
    validates :title,  # Validation method
      :presence => true
  end

  module ClassMethods
    def acts_as_article
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    ...
  end
end

ActiveRecord::Base.send :include, Article


# app/models/review.rb
class Review
  acts_as_article

  ...
end

Using the above code the plugin works. However if I add some Record Association in the Review class like this:

class Review
  acts_as_article

  has_many :comments # Adding association

  ...
end

and in my ReviewsController I add the following, as well:

def create
  ...

  @article.comments.build(   # This is the code line 89
    :user_id => @user.id
  )

  if @article.save
    ...
  end
end

I get this error

NoMethodError (undefined method `title' for #<Comments:0x00000103abfb90>):
  app/controllers/articles_controller.rb:89:in `create'

Probably it happens because the validation run for all Review “associated” classes\models and the Comment class doesn’t have the title attribute. I think that because if inside the plugin code I comment out the validation method like this

module Article
  ...

  included do
    # validates :title,  # Validation
    #   :presence => true
  end

  ...
end

I don’t get errors anymore.

So, how can I solve this issue?

Note: I am not expert on creating plugin (this is my first time), so I ask implicitly also if I’m doing a good job for the plugin implementation…

Answer 1

You are including validates_presence_of :title in ActiveRecord::Base, and thus every active record model is picking it up. Instead, you should do:

# vendor/plugins/article/lib/acts_as_article.rb
module Article
  extend ActiveSupport::Concern

   module ClassMethods
    def acts_as_article
      validates :title,  # Add validation method here
        :presence => true
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    ...
  end
end

So that you only include the validation on ActiveRecord models that expect the validation to go through. Let me know if this solves your issue.