How do you model “Likes” in rails?

Question

I have 3 models: User, Object, Likes

Currently, I have the model: a user has many Objects. How do I go about modeling:

1) A user can like many objects

2

Answer 1

You are close; to use a :through, relation, you first must set up the relationship you're going through:

class User < ActiveRecord::Base
  has_many :likes
  has_many :objects, :through => :likes
end

class Likes < ActiveRecord::Base
  belongs_to :user
  belongs_to :object
end

class Objects < ActiveRecord::Base
  has_many :likes
  has_many :users, :through => :likes    
end

Note that Objects should has_many :likes, so that the foreign key is in the right place. (Also, you should probably use the singular form Like and Object for your models.)

Answer 2

Here is a simple method to achieve this. Basically, you can create as many relationships as needed as long as you specify the proper class name using the :class_name option. However, it is not always a good idea, so make sure only one is used during any given request, to avoid additional queries.

class User < ActiveRecord::Base
  has_many :likes, :include => :obj
  has_many :objs
  has_many :liked, :through => :likes, :class_name => 'Obj'
end

class Like < ActiveRecord::Base
  belongs_to :user
  belongs_to :obj
end

class Obj < ActiveRecord::Base
  belongs_to :user
  has_many :likes, :include => :user

  has_many :users, :through => :likes

  # having both belongs to and has many for users may be confusing 
  # so it's better to use a different name

  has_many :liked_by, :through => :likes, :class_name => 'User'   
end


u = User.find(1)
u.objs # all objects created by u
u.liked # all objects liked by u
u.likes # all likes    
u.likes.collect(&:obj) # all objects liked by u


o = Obj.find(1)
o.user # creator
o.users # users who liked o
o.liked_by # users who liked o. same as o.users
o.likes # all likes for o
o.likes.collect(&:user)

Answer 3

To elaborate further on my comment to Brandon Tilley's answer, I would suggest the following:

class User < ActiveRecord::Base
  # your original association
  has_many :things

  # the like associations
  has_many :likes
  has_many :liked_things, :through => :likes, :source => :thing
end

class Like < ActiveRecord::Base
  belongs_to :user
  belongs_to :thing
end

class Thing < ActiveRecord::Base
  # your original association
  belongs_to :user

  # the like associations
  has_many :likes
  has_many :liking_users, :through => :likes, :source => :user
end

Answer 4

Models & associations as per naming conventions of rails modeling

class User < ActiveRecord::Base
  has_many :likes
  has_many :objects, :through => :likes
end

class Like < ActiveRecord::Base
  belongs_to :user
  belongs_to :object
end

class Object < ActiveRecord::Base
  belongs_to :user

  has_many :likes
  has_many :users, :through => :likes    
end

Also, you can use of already built-in gems like acts-as-taggable-on to have same functionality without code :)