On_delete options (CASCADE, PROTECT, SET_NULL) in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the CASCADE option do in Django's on_delete?

The CASCADE option deletes all related objects automatically when the referenced object is deleted. It's like a chain reaction removing dependent data.

beginner

Explain the PROTECT option in Django's on_delete.

PROTECT prevents deletion of the referenced object if there are related objects pointing to it. It raises an error to protect data integrity.

beginner

What happens when you use SET_NULL in Django's on_delete?

Using SET_NULL sets the foreign key field to NULL when the referenced object is deleted. The related object stays but loses the link.

intermediate

Which on_delete option requires the foreign key field to allow NULL values?

SET_NULL requires the foreign key field to have null=True because it sets the field to NULL on deletion.

intermediate

Why would you choose PROTECT over CASCADE in Django?

You choose PROTECT to avoid accidental deletion of important data. It forces you to handle related objects before deleting the main one.

What does on_delete=models.CASCADE do when the referenced object is deleted?

A Deletes all related objects automatically

B Prevents deletion and raises an error

C Sets the foreign key to NULL

D Does nothing to related objects

CASCADE deletes related objects automatically to keep data consistent.

Which on_delete option stops deletion if related objects exist?

A SET_NULL

B CASCADE

C DO_NOTHING

D PROTECT

PROTECT raises an error to prevent deletion if related objects exist.

When using SET_NULL, what must be true about the foreign key field?

A It must have <code>null=True</code>

B It must be unique

C It must be indexed

D It must have <code>blank=True</code>

SET_NULL sets the field to NULL, so null=True is required.

If you want to keep related objects but remove their link to a deleted object, which on_delete do you use?

A CASCADE

B SET_NULL

C PROTECT

D RESTRICT

SET_NULL removes the link by setting the foreign key to NULL.

Which on_delete option can cause a chain of deletions?

A SET_NULL

B PROTECT

C CASCADE

D DO_NOTHING

CASCADE deletes related objects, which can trigger further deletions.

Describe the differences between CASCADE, PROTECT, and SET_NULL in Django's on_delete.

Think about what happens to related objects when the main object is deleted.

When would you use PROTECT instead of CASCADE or SET_NULL?

Consider situations where deleting related data could cause problems.