n:m self-join with ruby on rails active record

问题

I'm trying to accomplish the following with ruby on rails, and I have problems to get the model-configuration right:

I would like to model possible connections between airports. I created the following models:

> rails generate model airport city name
> rails generate model connection airport_id destination_id

But most of the n:m association examples deal with associations between two different models on the one hand, or self-referencing models on the other hand, but I want to model a n:m association of models in one table between each other.

I would like to do something like that:

ny = Airport.create({"city" => "New York"})
la = Airport.create({"city" => "Los Angeles"})

ny.destinations << la
la.destinations << ny

I could not find any example on how to do this.

Does anyone have an idea how to accomplish something like that with active record?

The following article from railscasts seems to help: http://railscasts.com/episodes/163-self-referential-association

app/models/airport.rb

class Airport < ActiveRecord::Base
  attr_accessible :city, :name

  has_many :connections
  has_many :destinations, :through => :connections
  has_many :inverse_connections, :class_name => "Connection", :foreign_key => "destination_id"
  has_many :inverse_destinations, :through => :inverse_connections, :source => :airport
end

app/models/connection.rb

class Connection < ActiveRecord::Base
  attr_accessible :airport_id, :destination_id

  belongs_to :airport
  belongs_to :destination, :class_name => "Airport"
end

Why is it called "inverse_"? Do you think thats the best solution to the problem or could you think of a better solution? What about performance / index?

best regards Andreas

来源：https://stackoverflow.com/questions/16388623/nm-self-join-with-ruby-on-rails-active-record