Question

In Rails 3 I’m trying to model a user content system, where the user can post different types of content, for example, note, photo, url etc.

From a Java/C# OO perspective, I would use a polymorphic relationship between the User and an interface representing a Content item, e.g. something called IUserContent.

I’m struggling to find an example that works how I expect it to, here’s what I tried first, in short I’m getting confused about the implementation of polymorphic associations in ActiveRecord.

# user.rb model - includes...

has_many :notes, :as => :postable, :dependent => :destroy, :inverse_of => :postable
has_many :urls, :as => :postable, :dependent => :destroy, :inverse_of => :postable
has_many :photos, :as => :postable, :dependent => :destroy, :inverse_of => :postable


# url.rb ... 

belongs_to :postable, :polymorphic => true, :inverse_of => :urls


# photo.rb

belongs_to :postable, :polymorphic => true, :inverse_of => :photos


# note.rb

belongs_to :postable, :polymorphic => true, :inverse_of => :notes

I’m still just following examples I’ve found, and frankly this feels like User is the polymorphic target, not the content.

I think I want something like this…

# within user.rb

has_many :postable, :as => :postable, dependent => :destroy, :inverse_of => :users

# photo.rb 
# url.rb
# note.rb
# all have the following...

belongs_to :user, :polymorphic => true, :inverse_of => :postable

… looking for a few pointers in the right direction.

Thank you.

Answer 1

The only way you can do that is if all of these classes inherit from the same base class, as in:

class User < ActiveRecord::Base
  has_many :postable, :as => :postable, :dependent => :destroy, :class_name => 'Postable'
end

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

class Photo < Postable
end

class Url < Postable
end

class Note < Postable
end

So, you have to use the ActiveRecord single-table inheritance to model such a relationship.