Association callbacks in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are association callbacks in Rails?

Association callbacks are special methods that run automatically when you add or remove objects from an association, like has_many or has_one. They help you run code during these changes.

beginner

Name two common association callbacks in Rails.

Two common association callbacks are before_add and after_remove. They run before adding an object to an association and after removing an object, respectively.

intermediate

How do you define a before_add callback on a has_many association?

You add it inside the association like this:<br>has_many :comments, before_add: :check_comment<br>Then define the method check_comment in your model to run before adding a comment.

intermediate

What happens if a before_add callback throws an exception?

If a before_add callback raises an error, the object will NOT be added to the association. This lets you stop unwanted changes safely.

intermediate

Can association callbacks access the object being added or removed? How?

Yes, association callbacks receive the object being added or removed as an argument. For example:<br>before_add :method_name where method_name(added_object) can use that object inside.

Which callback runs before adding an object to a Rails association?

A before_add

B after_add

C before_save

D after_remove

The before_add callback runs right before an object is added to an association.

What argument does an association callback method receive?

A No arguments

B The parent model

C The object being added or removed

D The database connection

Association callbacks receive the object being added or removed as an argument.

If a before_add callback raises an error, what happens?

A The object is not added

B The object is still added

C The callback is ignored

D The entire transaction rolls back

Raising an error in before_add stops the object from being added.

Which association type supports before_add callbacks?

A All of the above

B has_many

C has_one

D belongs_to

before_add is commonly used with has_many associations.

Where do you specify association callbacks in Rails?

A In the routes file

B In the controller

C In the database schema

D Inside the association declaration

You specify callbacks like before_add inside the association declaration in the model.

Explain what association callbacks are and give an example of when you might use one.

Think about how Rails lets you run code when you add or remove related objects.

Describe how to add a before_add callback to a has_many association and what happens if the callback raises an error.

Focus on the association declaration and callback behavior.