belongs_to relationship in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the belongs_to association represent in Rails?

It represents a connection where a model holds a reference to another model, meaning each instance belongs to one instance of another model.

beginner

In a belongs_to relationship, where is the foreign key stored?

The foreign key is stored in the model that declares belongs_to. This key points to the associated model's primary key.

beginner

How do you declare a belongs_to association in a Rails model?

Inside the model class, write belongs_to :other_model_name to set up the association.

intermediate

What happens if you try to save a model with a belongs_to association but the foreign key is missing?

By default, Rails will raise a validation error because belongs_to requires the associated object to be present unless specified otherwise.

intermediate

Can a belongs_to association be optional in Rails? How?

Yes, by adding optional: true to the belongs_to declaration, the association can be saved without the foreign key.

Where is the foreign key stored in a belongs_to association?

A In the model declaring <code>belongs_to</code>

B In the model declaring <code>has_many</code>

C In a join table

D In the database schema only

The foreign key is stored in the model that declares belongs_to, linking it to the associated model.

What does belongs_to :user mean inside a model?

A This model has many users

B This model is unrelated to users

C This model belongs to one user

D This model owns the user model

It means each instance of this model is linked to one user instance.

How do you make a belongs_to association optional?

A Add <code>optional: true</code> to the association

B Add <code>required: false</code> to the association

C Remove the foreign key column

D Use <code>has_one</code> instead

Adding optional: true allows saving the model without the associated record.

If a model belongs_to :post, what foreign key column is expected?

A <code>post_key</code>

B <code>post_id</code>

C <code>post_fk</code>

D <code>postRef</code>

Rails expects the foreign key column named post_id by convention.

What validation does Rails add by default to belongs_to associations?

A No validation by default

B Uniqueness validation

C Length validation

D Presence validation of the associated object

Rails requires the associated object to be present unless optional: true is set.

Explain how the belongs_to association works in Rails and where the foreign key is stored.

Think about which model 'owns' the reference.

Describe how to make a belongs_to association optional and why you might want to do that.

Consider cases where the related object might not exist yet.