gistfile1.rb

class Like < ActiveRecord::Base
  belongs_to :likeable, polymorphic: true
  belongs_to :user
end

class Project < ActiveRecord::Base
  has_many :likes, as: :likeable
end

class Source < ActiveRecord::Base
  has_many :likes, as :likeable
end

class User < ActiveRecord::Base
  has_many :likes, inverse_of: :user
end