Ruby on Rails: two has_many same_models :through => different_model

Question

I'd like to create 2 has_many on the same model but that goes through a different model (which is a join table)

Here's the code:

class Content
  belongs_to :dis
  belongs_to :fac

  has_many :dis_representations, :through => :dis
  has_many :fac_representations, :through => :fac
end

class Fac
  has_many :fac_representations
  has_many :contents
end

class Dis
  has_many :dis_representations
  has_many :contents
end

class DisRepresentation
  belongs_to :user, :foreign_key => "e_user_id"
  belongs_to :dis
end

class FacRepresentation
  belongs_to :user, :foreign_key => "e_user_id"
  belongs_to :fac
end

class User
  has_many :dis_representations, :foreign_key => "e_user_id"
  has_many :fac_representations, :foreign_key => "e_user_id"
  has_many :dises, :through => :dis_representations
  has_many :facs, :through => :fac_representations
  has_many :contents, :through => :dises, :source => :contents
  has_many :contents, :through => :facs :source => :contents
end

Now I'd like to do this:

User.first.contents

If I do this, it almost works. The only problem is that only the second has_many :contents get's called.

Now I could solve it by creating a method like this:

def contents
    (dises + facs).map(&:contents).flatten
end

However, I loose all contents scopes if I do the above because contents becomes a simple array.

Is there any way around this? Maybe I'm using a completely wrong approach. Is there another way?

Thanks

Answer 1

If the dis and fac models are not significantly different then you could collapse them into a single set of models and introduce a 'type' attribute that lets you discriminate between these different types of content. Then you won't have an issue when trying to query it (it's only going to get worse as you want to write more complex queries) and it'll scale when you want to add more content types.

Answer 2

I'd use two different names for the contents associations, like dis_contents and fac_contents.

If you want to retrieve all Content objects with a single association, you should change your associations and use a polymorphic join table.

Maybe this example would help

has_many :through + polymorphic relationships