Polymorphic Associations in Ruby on Rails

Zahid Ali — Sun, 11 Dec 2022 21:17:06 +0000

In Ruby on Rails, a polymorphic association is a type of association that allows a model to belong to more than one other model on a single association. This is useful when you have a model that can be associated with multiple other models in a single association.

Here is an example of using a polymorphic association to define a relationship between a Comment model and both a Post and a Video model:

class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true
end

class Post < ApplicationRecord
  has_many :comments, as: :commentable
end

class Video < ApplicationRecord
  has_many :comments, as: :commentable
end

In this example, the Comment model belongs_to a commentable model using a polymorphic association. This means that a Comment can belong to either a Post or a Video model, depending on the value of the commentable_type attribute. The Post and Video models both has_many Comment objects, specifying that they are the commentable type for those Comment objects.

Once the associations are defined, you can use them to access the associated objects in your code. For example, you can use the post.comments method to access the Comment objects associated with a Post object:

post = Post.find(1)
post.comments    # => Returns an array of `Comment` objects associated with the `Post`

You can also use the video.comments method to access the Comment objects associated with a Video object:

video = Video.find(1)
video.comments    # => Returns an array of `Comment` objects associated with the `Video`

Overall, polymorphic associations are a useful way to define relationships between models in Ruby on Rails when a model can belong to multiple other models on a single association. By using polymorphic associations, you can easily access and manipulate the associated objects in your code.

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Polymorphic Associations in Ruby on Rails