rails：这个关联条件的多重连接有什么问题？

Here are my models:

这是我的模特:

class Deck < ActiveRecord::Base
  belongs_to :game
  has_many :deck_cards
end

class DeckCard < ActiveRecord::Base
  belongs_to :card
  belongs_to :deck
end

class Card < ActiveRecord::Base
end
class Deck < Ac