Polymorphic Association with multiple associations on the same model

问题

I'm slightly confused about a polymorphic association I've got. I need an Article model to have a header image, and many images, but I want to have a single Image model. To make matters even more confusing, the Image model is polymorphic (to allow other resources to have many images).

I'm using this association in my Article model:

class Article < ActiveRecord::Base
  has_one :header_image, :as => :imageable
  has_many :images, :as => :imageable
end

Is this possible? Thanks.

回答1:

Yep. That's totally possible.

You might need to specify the class name for header_image, as it can't be inferred. Include :dependent => :destroy too, to ensure that the images are destroyed if the article is removed

class Article < ActiveRecord::Base
  has_one :header_image, :as => :imageable, :class_name => 'Image', :dependent => :destroy
  has_many :images, :as => :imageable, :dependent => :destroy
end

then on the other end...

class Image < ActiveRecord::Base
  belongs_to :imageable, :polymorphic => true
end

回答2:

I tried this, but then header_image returns one of the images. Simply because the images table doesn't specify a different image use type (header_image vs. normal image). It simply says: imageable_type = Image for both uses. So if there's no information stored about the use type, ActiveRecord cannot differentiate.

来源：https://stackoverflow.com/questions/1168047/polymorphic-association-with-multiple-associations-on-the-same-model