Question

I have two tables for tagging so that I can attach tags to any models, it works likes so…

There’s a tagged item join table which has a tag_id column and then two other columns for polymorphism: taggable_type and taggable_id…

class TaggedItem < ActiveRecord::Base
  attr_accessible :taggable_id, :taggable_type, :tag_id

  belongs_to :taggable, :polymorphic => true
  belongs_to :tag
end

There’s also all of the things that can have tags, for example here’s a product and image model with tags attached:

class Product < ActiveRecord::Base
  has_many :tagged_items, :as => :taggable, :dependent => :destroy
  has_many :tags, :through => :tagged_items
end

class Image < ActiveRecord::Base
  has_many :tagged_items, :as => :taggable, :dependent => :destroy
  has_many :tags, :through => :tagged_items
end

The problem is with the tag model, I can seem to get the reverse work, on the tag modle I want to have a has_many images and has_many products like so:

class Tag < ActiveRecord::Base
  has_many :tagged_items, :dependent => :destroy
  has_many :products, :through => :tagged_items
  has_many :images, :through => :tagged_items
end

This is causing an error, I was wondering how I can fix this. So the tag table works through the polymorphic tagged items table.

Any help would be much appreciated. Thanks!

Edit:

Could not find the source association(s) :product or :products in model TaggedItem. Try 'has_many :products, :through => :tagged_items, :source => <name>'. Is it one of :taggable or :tag?

Answer 1

The has_many :through associations in your Tag model are not able to get the source association for Product and Image from the TaggedItem Model. e.g. has_many :products, :through => :tagged_items will look for a direct association belongs_to :product in TaggedItem which in case of polymorphic association is written as belongs_to :taggable, :polymorphic => true. So for the Tag model to understand exact source of the association we need to add an option :source and its type as :source_type

So change your Tag model associations to look like

class Tag < ActiveRecord::Base
  has_many :tagged_items, :dependent => :destroy
  has_many :products, :through => :tagged_items, :source => :taggable, :source_type => 'Product'
  has_many :images, :through => :tagged_items, :source => :taggable, :source_type => 'Image'
end

This should fix your problem. 🙂