Dependent destroy and nullify in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does dependent: :destroy do in a Rails association?

It deletes all associated child records when the parent record is deleted, ensuring no orphaned records remain.

beginner

What is the effect of dependent: :nullify in a Rails model association?

It sets the foreign key of associated child records to NULL instead of deleting them when the parent is deleted.

intermediate

When should you use dependent: :destroy instead of dependent: :nullify?

Use destroy when child records should be removed with the parent to keep data clean. Use nullify when child records should remain but lose their link to the deleted parent.

beginner

What happens if you don't specify any dependent option in a Rails association?

The associated child records remain unchanged when the parent is deleted, which can lead to orphaned records with invalid foreign keys.

intermediate

Explain the difference between dependent: :destroy and dependent: :delete_all.

destroy runs callbacks on each child before deleting, while delete_all deletes all children directly in the database without callbacks.

What does dependent: :nullify do when the parent record is deleted?

A Sets child records' foreign keys to NULL

B Deletes all child records

C Raises an error

D Does nothing

dependent: :nullify sets the foreign key in child records to NULL, keeping the child records but removing their link to the parent.

Which dependent option runs callbacks on child records before deletion?

A nullify

B destroy

C delete_all

D restrict_with_exception

dependent: :destroy runs callbacks on each child record before deleting it.

If you want to keep child records but remove their link to the parent, which option do you use?

A dependent: :restrict_with_error

B dependent: :destroy

C dependent: :delete_all

D dependent: :nullify

dependent: :nullify keeps child records but sets their foreign key to NULL.

What risk exists if you omit the dependent option in a has_many association?

A Orphaned child records may remain

B Child records are automatically deleted

C Parent record cannot be deleted

D Foreign keys are set to NULL

Without dependent, deleting a parent leaves child records with foreign keys pointing to a non-existent parent, causing orphaned records.

Which dependent option deletes child records directly in the database without callbacks?

A destroy

B nullify

C delete_all

D restrict_with_exception

dependent: :delete_all deletes child records directly in the database, skipping callbacks.

Describe how dependent: :destroy and dependent: :nullify affect child records when a parent record is deleted in Rails.

Think about whether child records are deleted or kept.

Explain why it is important to use the dependent option in Rails associations.

Consider what happens to child records when the parent is removed.