has_many在Rails中嵌套到许多模型

Question

I have 4 different models in rails and there is a has_many and belongs_to association between them. For example:

class Apple < AR::Base
  has_many :bananas
end

class Banana < AR::Base
  belongs_to :apple
  has_many :oranges
end

class Orange < AR::Base
  belongs_to :banana
  has_many :berries
end

class Berry < AR::Base
  belongs_to :orange
end 

Now, if I write, like @apple.berries , I should get the list of berries belongs to that Apple. So how should I define this association? One of my friend told me to use inverse polymorphic association. I don't know whether its related to the above issue or not.

Answer 1

What you actually need here is has_many + through relationship. Right now, an Apple object does contain Berry objects, but Apple object doesn't contain them directly. So we need to tell it explicitly like:

class Apple < ActiveRecord::Base
  has_many :bananas
  has_many :berries, through: :bananas
end

class Banana < ActiveRecord::Base
  belongs_to :apple
  has_many :oranges
  has_many :berries, through: :oranges
end

Now, you can berries directly on an Apple object as well as on a Banana object.