Question

for instance, I have 2 model Drummer and Video

If I use one-to-many association drummer has_many videos, and video belongs_to drummer,

So I can use the method in both side: video.drummers or drummer.videos

But when I use polymorphic association, which I think the right to for this, because, there will be a lot model have video, it makes sense make the video model polymorphic

I can use drummer.videos,
But I don’t know how to get which drummer the video belongs to

video.drummer doesn’t work,

anybody could tell me how to do this, and what’s other methods I can use after I set up the association.

Thanks

Answer 1

First, you need to add a migration file to add columns in videos:

class AddPolymorphicReferenceToVideos < ActiveRecord::Migration
  def self.up
    add_column :videos, :video_holder_id, :integer
    add_column :videos, :video_holder_type, :string
    add_index :videos, :video_holder_id
    add_index :videos, :video_holder_type
  end

  def self.down
    # just remove indexes and columns above
  end
end

Then you can add polymorphic association in Video model:

class Video < ActiveRecord::Base
  belongs_to :video_holder, :polymorphic => true
end

And change your Drummer like this:

class Drummer < ActiveRecord::Base
  has_many :videos, :as => :video_holder
end

Now you can use the polymorphic association:

drummer.videos  # => an videos array
video.video_holder  # => a model holds the video