How can I use Mongoid and ActiveRecord in parallel in Rails 3?

Question

I\'m using rails 3, and began my application with ActiveRecord. Now, I have many models, and the relations are starting to get complicated, and some could be more simply expres

Answer 1

I don't see any reason why you couldn't have both ActiveRecord and Mongoid models in the same application. That being said, I'm almost certain that you'll run into issues if you try to create relationships between your ActiveRecord and Mongoid models.

If your ActiveRecord models are heavily inter-related, but better suited to a document structure, then I would suggest just biting the bullet and converting them all to Mongoid documents. I had to do this recently on a (large-ish) project, and it's significantly less stressful than you would think.

If you have good unit tests for your models, then it should be a total snap. If you don't - write your unit tests first, make sure they pass with ActiveRecord and then start migrating things over to Mongoid.

Answer 2

What I did was just mock the relationship with methods in each the AR model and the Mongoid model like so.

# visit_session.rb
class VisitSession
  include Mongoid::Document
  include Mongoid::Timestamps

  field :user_id, type: Integer
  index({user_id: 1},{name: :user_id_index})

  # Mock a belongs_to relationship with User model
  def user
    User.find(self.user_id)
  end
end

# user.rb
class User < ActiveRecord::Base

  # Mock a has_many relationship with VisitSession Mongoid model
  def visit_sessions
    VisitSession.where(user_id: self.id)
  end
end

Of course you won't have all the AR methods on VisitSession Mongoid model but you'll at least be able to mock the relationship between the two fairly well.

Hope this helps.

Answer 3

i created a module for spoofing the relation in active record models.

module MongoRelations
  def belongs_to_mongo(name, options = {})
    id_name = "mongo_#{name}_id".to_sym
    mongo_model = options[:through] || "Mongo::#{name.to_s.camelize}".constantize

    define_method(name) do
      id = send(id_name)
      mongo_model.find(id) if id.present?
    end

    define_method("#{name}=") do |value|
      send("#{id_name}=".to_sym, value.try(:id).to_s)
    end
  end
end

In my SQL table, I name my mongo relations using the convention mongo_XXX_id, instead of XXX_id

I also namespace all my mongo models under Mongo::

in my active record model

class Foo < ActiveRecord::Base
    belongs_to_mongo :XXX
end

which allows

Foo.new.XXX = Mongo.find('123')
Foo.XXX

or

Foo.new.XXX_id = '123'
Foo.XXX

Answer 4

... just for tracking purpose, I'd like to add something I just found out on this field:

DRY up your SQL+NoSQL Rails projects