Question

I’m new to Rails and Ruby. I’m trying to implement Data-Context-Interaction /aka DCI/ paradigm in Rails 3.2.11 app. I have User model which one-to-many association with Topic model. I’m trying to write a mixin to User, but they’re not working, please can you offer some debugging help.

My mixing looks like:

module Speaker

  extend ActiveSupport::Concern

  included do
    has_many :assigned_topics, class_name: 'Topic', foreign_key: 'speaker_id'
  end

  def add_topic(topic)
    topic.speaker = self
    topic.save
  end

  def remove_topic(topic)
    topic.speaker = nil
    topic.save
  end
end

When I run below code I get an error:

u = User.first
u.extend Speaker
u.assigned_topics
NoMethodError: undefined method `assigned_topics' for #<User:0x00000002f5dca8>

Answer 1

Do NOT use the DCI pattern in Rails. At least if you expect to get some traffic. Extending an existing object is currently terribly slow. It crashes the caching mechanism of every single ruby implementation.

I know there was some fuzz about this overrated stuff during the last weeks, but really: do not use it this way. It’s only a big hassle and much drama around. Rails is not a Java framework, and therefore it hasn’t the same problems like Java.

If you want to move stuff from models to modules, use a simple concern, and include it hardcoded in the model(s). No live-extend at runtime and all the hoops. Here is a gist from @dhh how to use it: https://gist.github.com/1014971