Polymorphic associations in Rails are a powerful feature that allow a single association to belong to multiple types of models. This can be useful in many scenarios, such as when you have a comment system that can be used on multiple types of objects (e.g. posts, articles, photos, etc.), or when you have an attachment system that can be used on multiple models (e.g. users, products, blog posts, etc.).

        In this blog, we'll explore how to implement polymorphic associations in Rails and some common use cases.

Implementation

        To implement a polymorphic association in Rails, we use a combination of a foreign key and a type column. For example, let's say we have a comments system that can be used on both posts and articles. We would start by creating a comments table with the following columns:

class CreateComments < ActiveRecord::Migration[6.0]
  def change
    create_table :comments do |t|
      t.text :content
      t.references :commentable, polymorphic: true
      t.timestamps
    end
  end
end

        The commentable column is a foreign key that references either a Post or an Article, depending on the type of object the comment is associated with. The polymorphic: true option tells Rails that this association is polymorphic.

        Next, we would create the Post and Article models and define the association:

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

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

        The as: :commentable option tells Rails that this association is polymorphic and that the foreign key column is named commentable.

        Finally, we can create a comment for either a post or an article like this:

post = Post.find(1)
comment = post.comments.create(content: "Great post!")

article = Article.find(1)
comment = article.comments.create(content: "Great article!")

        In this example, the create method automatically sets the commentable_id and commentable_type columns based on the type of object the comment is associated with.