Question

I am new to association.any one explain me where to use polymorphic association and its
purpose .

class Picture < ActiveRecord::Base
belongs_to :imageable, :polymorphic => true
end

class Employee < ActiveRecord::Base
has_many :pictures, :as => :imageable
end

class Product < ActiveRecord::Base
has_many :pictures, :as => :imageable
end

Thanks in advance.

Answer 1

polymorphic association is used when the parent or child object class is not known.

eg

A has_many :cs, :as => resource, :dependent => :destroy
B has_many :cs, :as => resource, :dependent => :destroy

C belongs_to :resource, :polymorphic => true

here, C may either belong to A or B.

see http://guides.rubyonrails.org/association_basics.html#polymorphic-associations for more information.