Ruby on Rails Polymorphic Associations Explained

Sometimes a single model needs to connect with multiple other models — not just one specific type. That’s where polymorphic associations come in.

How It Works

Polymorphic associations use two database columns:

1. One storing the related model’s ID
2. Another capturing that model’s type (class name)

This allows a single association to point to different model types dynamically.

Real-World Applications

• E-commerce — products to attachments (images, videos, documents)
• Inventory Management — shipments to different item types
• CMS — files attached to different content types (articles, pages, comments)

Implementation

class Attachment < ApplicationRecord
  belongs_to :attachable, polymorphic: true
end

class Product < ApplicationRecord
  has_many :attachments, as: :attachable
end

class Article < ApplicationRecord
  has_many :attachments, as: :attachable
end

The migration creates the polymorphic columns:

create_table :attachments do |t|
  t.references :attachable, polymorphic: true
  t.timestamps
end

When to Use Polymorphic Associations

Use them when you have a model that logically belongs to multiple different parent types. Common examples include comments, attachments, tags, and activity logs.

Conclusion

Polymorphic associations are a powerful Rails feature that reduces code duplication and keeps your data model clean. Use them when a single model needs to relate to multiple other models in the same way.