Searching polymorphic associations in Rails

Question

Hello all,

I have a need in my app to allow users to bookmark a post. They should only be able to create one bookmark per post. I've set up my polymorphic association like so:

class Post < ActiveRecord::Base
  has_many :bookmarks, :as => :bookmarkable
end

class Bookmark < ActiveRecord::Base
  belongs_to :bookmarkable, :polymorphic => true
  belongs_to :user
end

class User < ActiveRecord:Base
  has_many :posts
  has_many :bookmarks
end

In my view, a user can create a bookmark. I would like to find some way to replace the "Create Bookmark" view code with "Delete Bookmark" code, if the user has already bookmarked a particular post.

If I try to do something like this:

@post = Post.find(params[:id, :include => [:bookmarks]])
- if @post.bookmarks.users.include?(@user)

I get a No Method error for "users"

How can I access owners of the bookmarks, to determine if the current user has already bookmarked a page?

Thank you.

Answer 1

I would approach this from the user's point of view:

class User < ActiveRecord::Base
  has_many :posts
  has_many :bookmarks

  # Rails 3
  def bookmarked?(post)
    bookmarks.where(
      {
        :bookmarkable_id => post.id, :bookmarkable_type => post.class.name
      }
    ).count > 0
  end

  # Rails 2
  def bookmarked?(post)
    bookmarks.find(:all, :conditions => 
      {
        :bookmarkable_id => post.id, :bookmarkable_type => post.class.name
      }
    ).count > 0
  end
end

if @user.bookmarked?(@post)
  # Show delete link
else
  # Show bookmark link
end

I would also advice you to add a validation to your bookmarks model that prevents a user from bookmarking the same post twice.