You might have instances where the associations could be with multiple models. For example, if you have a Picture model that can be associated with either a Student model or an Employee model. In this case, you really want to be able to call @picture.imageable to get the image. This is where polymorphic associations come in.
class Picture < ActiveRecord::Base belongs_to :imageable, :polymorphic => true end class Student < ActiveRecord::Base has_many :pictures, :as => :imageable end class Employee < ActiveRecord::Base has_many :pictures, :as => :imageable end
You can think of a polymorphic belongs_to declaration as setting up an interface that any other model can use.
You can also retrieve a collection of pictures: @student.pictures or @employee.pictures from instances of Student or Employee model.
To make this work, you need to declare both a foreign key column and a type column in the model that declares the polymorphic interface:
class CreatePictures < ActiveRecord::Migration
def self.up
create_table :pictures do |t|
t.string :name
t.integer :imageable_id
t.string :imageable_type
t.timestamps
end
end
def self.down
drop_table :pictures
end
end
Finally, you can read more on the documentation written by Rails team.
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