Wrong sql request done with a "has_many" for a subclass

Question

I'm trying to implement a "facebook like" like relationship. I wanted to use inheritance for that, so here's my structure :

Likes with a user_id:integer attribute |> PostsLike that inherits Like with a post_id:integer attribute

So here's my Like.rb model :

class Like < ActiveRecord::Base
  belongs_to :user
end

And then my PostLike.rb model :

class Postlike < Like
  belongs_to :post
end

And finally I have a post model that will have multiple postlikes objects :

class Post < ActiveRecord::Base

  has_many :postlikes

end

But here's my problem, when I go into irc and that :

1. I get a Post object :

   ruby-1.9.2-p290 :001 > @p = Post.all.first

2. I try to get postlikes of this object, here's the sql statement :

   SELECT likes.* FROM likes WHERE likes.type IN ('Postlike') AND likes.post_id = 310

So basically instead of doing

postlikes.post_id

Rails' doing

likes.post_id

Any idea to fix that ?

Answer 1

ActiveRecord stores Like and Postlike object in the same table named "likes", and uses a column named "type" to save the class of the object. That explains the statement:

WHERE likes.type IN ('Postlike') AND likes.post_id = 310

There is no table postlikes

See "Single table inheritance" chapter at http://api.rubyonrails.org/classes/ActiveRecord/Base.html