Mongoid的has_one多态关联逆

Question

I have a following model structure. I have an Itinerary that has many itinerary nodes. Each itinerary node is a wrapper around either a place, hotel, activity etc. So for example.

Itinerary = "Trip to Paris" Itinerary.itinerary_nodes = [Node1, Node2, Node3] where Node1 = "JFK Airport" Node2 = "CDG Airport" Node3 = "Eiffel Tower"

So essentially nodes represents the places you will visit in your itinerary. In my model structure; lets assume that my airports are modeled different from monuments or hotels. Now I want to create a association such that;

class ItineraryNode
  include Mongoid::Document
  has_one :stopover
end

Where each stopover can be a different object. It's type and id is stored by default and is later inflated using that.

So how do I declare multiple models to be associated to ItineraryMode? I can implement this specifically by ensuring that I set these attributes manually in initializer; but curious if something like this is supported by default.

Cheers

Answer 1

This is not a "has_one", it is a "belongs_to" (polymorphic)

class ItineraryNode
  include Mongoid::Document
  belongs_to :stopover, :polymorphic => true
  belongs_to :itinerary
end

class Airport
  include Mongoid::Document
  has_many :itinerary_nodes, :as => :stopover
end

class Place
  include Mongoid::Document
  has_many :itinerary_nodes, :as => :stopover
end

So now you can get:

@itinerary.itinerary_nodes.each do |node|
  if node.stopover.is_a? Airport
    puts "Welcome to #{note.stopover.name}"
  elsif node.stopover.is_a? Event
    puts "Bienvenue, would you like a drink?"
  elsif node.stepover.is_a? Place
    puts "The ticket line is over there"
  end
end

(I used an if construct just to show better the polymorphism, you would use a case construct here...)

You see that node.stepover can be of many classes.

EDIT (after the comment, I understand that the ItineraryNode model is an attempt to a handcrafted polymorphism for a many-to-many association.

From the Mongoid documentation:

Polymorhic behavior is allowed on all relations with the exception of has_and_belongs_to_many.

So you need to use an intermediate model ( ItineraryNode ). The provided solution is the simplest one I can think of.