Polymorphic associations in reverse?

My app has an association that’s got me scratching my head.

I have Users, and Images. A User has many Images. (Yes, another
picture sharing app, but it’s for a small niche, and it doesn’t end
in -r!)

I would like to express a “Favorite” relationship between both Users
to Users, and Users to Images. This seems like the opposite of the
standard polymorphic model, i.e. tags and taggable, where a Tag may
apply to many different types of Thing.

Perhaps I’m not thinking of it properly, but this was my first stab
at the relationship:

###############################################################
class Image < ActiveRecord::Base

Can be a favorite

belongs_to :favorite
belongs_to :favorable, :polymorphic => :true
end

class User < ActiveRecord::Base
has_many :images

Can be a favorite

belongs_to :favorite
belongs_to :favorable, :polymorphic => :true

Has many favorite ‘things’

has_many :favorites, :dependent => :destroy
has_many :favorite_images, :as => :favorable, :through => :favorites,
:classname => “Image”
has_many :favorite_users, :as => :favorable, :through => :favorites,
:classname => “User”
end

class Favorite < ActiveRecord::Base
belongs_to :favorable, :polymorphic => true
end

create_table “favorites” do |t|
t.column :user_id, :integer
t.column :favorable_id, :integer
t.column :favorable_type, :string
end

create_table “images” do |t|
t.column :name, :string
end

create_table “users” do |t|
t.column :name, :string
end
###############################################################

This is of course wrong and does not work :slight_smile: But I don’t know
whether I’m thinking of the problem incorrectly, or whether there’s
even a proper way to do this sort of reverse-polymorphic-join in
ActiveRecord.

Does anyone have any advice?

-Seth

The main page on polymorphic associations on the wiki actually is a
reverse relationship (folder has many textfiles, images, etc, from
memory). I found it very helpful:
http://wiki.rubyonrails.com/rails/pages/HowToUsePolymorphicAssociations

Seth Morabito wrote:

My app has an association that’s got me scratching my head.

I have Users, and Images. A User has many Images. (Yes, another
picture sharing app, but it’s for a small niche, and it doesn’t end
in -r!)

I would like to express a “Favorite” relationship between both Users
to Users, and Users to Images. This seems like the opposite of the
standard polymorphic model, i.e. tags and taggable, where a Tag may
apply to many different types of Thing.

Have to say I’d be tempted to split the two types of favourite for
simplicities sake.

Say, Favourites and Contacts (for example).

A.

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