Question

I am quite new to mongoDB and I’m just using it for a new rails project I’m working on.
What I wanted to do now is, having an (embedded) document reference another collection, but with different roles.

Somehow this doesn’t seem to work. I know, that I can’t define a relation from an external collection to my embedded one. So in my case, I cannot acces the Locations from my User and I’m fine with that. Still, I need to define the referenced_in :location part, because otherwise I get an error message undefined method 'name' for nil:NilClass when I try to add a new Location to the Place.

So that’s just the preface. My actual problem is, that these roles thing doesn’t seem to work. When I create a new Location like that in a Place locations.create(:user_a => some_user), then also user_b is set to that user.

Is there any way to make this working? Or am I doing something wrong?

class Place
  include Mongoid::Document
  embeds_many :locations
end

class Location
  include Mongoid::Document
  embedded_in :place, :inverse_of => :locations
  references_one :user_a, :class_name => "User" #, :stored_as => :array
  references_one :user_b, :class_name => "User" #, :stored_as => :array
end

class User
  include Mongoid::Document
  referenced_in :location, :inverse_of => :dropper
  referenced_in :location, :inverse_of => :picker
end

Answer 1

I think you have to disambiguate the two location associations (because the reference is stored on the referenced_in side):

class User
  include Mongoid::Document
  referenced_in :location_a, :inverse_of => :user_a, :class_name => "Location"
  referenced_in :location_b, :inverse_of => :user_b, :class_name => "Location"
end

I can’t help feeling that there may be a better way to do this though…

Is this a better approach?

class Location
  include Mongoid::Document
  embedded_in :place, :inverse_of => :locations
  referenced_in :user_a, :class_name => "User"
  referenced_in :user_b, :class_name => "User"
end

class User
  include Mongoid::Document
end