Polymorphic associations in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a polymorphic association in Rails?

A polymorphic association lets a model belong to more than one other model using a single association. It uses a type and an ID to link to different models through one interface.

beginner

How do you declare a polymorphic belongs_to association in Rails?

Use belongs_to :attachable, polymorphic: true in the model that belongs to multiple other models.

beginner

What columns are required in the database for a polymorphic association?

You need two columns: one for the ID (e.g., <code>attachable_id</code>) and one for the type (e.g., <code>attachable_type</code>) to store the associated model's class name.

intermediate

How do you set up the other side of a polymorphic association?

Use has_many :attachments, as: :attachable in the models that can have attachments. The as: option tells Rails this is a polymorphic interface.

intermediate

Why use polymorphic associations instead of multiple separate associations?

Polymorphic associations reduce code duplication and database complexity by allowing one model to relate to many others without needing separate foreign keys or tables for each.

Which two columns are essential for a polymorphic association in Rails?

A attachable_key and attachable_name

B attachable_id and attachable_type

C attachable_key and attachable_type

D attachable_id and attachable_name

Rails uses attachable_id to store the associated record's ID and attachable_type to store the class name.

How do you declare a polymorphic association on the model that belongs to multiple models?

A belongs_to :attachable, polymorphic: true

B has_one :attachable, polymorphic: true

C has_many :attachable, polymorphic: true

D belongs_to :attachable

The model that belongs to multiple others uses belongs_to :attachable, polymorphic: true.

What does the as: option do in a has_many association?

A Declares a scope

B Specifies the foreign key name

C Sets the table name

D Defines the polymorphic interface name

The as: option tells Rails the name of the polymorphic interface to use.

Which of these is a benefit of polymorphic associations?

A They simplify code by using one association for many models

B They require more database tables

C They prevent models from sharing associations

D They only work with one model

Polymorphic associations let one model relate to many others through a single association, simplifying code.

If a Comment model belongs to either a Post or a Photo, what would the polymorphic association look like in Comment?

A has_many :commentable, polymorphic: true

B belongs_to :post_or_photo

C belongs_to :commentable, polymorphic: true

D has_one :commentable

The Comment model uses belongs_to :commentable, polymorphic: true to belong to either Post or Photo.

Explain how polymorphic associations work in Rails and why they are useful.

Think about how one model can connect to many different models using one link.

Describe the database setup needed to support a polymorphic association in Rails.

Focus on the columns that store the link to other models.