On_delete options (CASCADE, PROTECT, SET_NULL) in Django - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delete related objects automatically when the referenced object is deleted.

Django

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    author = models.ForeignKey(Author, on_delete=models.[1])
    title = models.CharField(max_length=200)

Drag options to blanks, or click blank then click option'

ACASCADE

BPROTECT

CSET_NULL

DDO_NOTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using PROTECT will prevent deletion instead of deleting related objects.

Using SET_NULL requires the field to allow null values.

Using CASCADE deletes all related Book objects when an Author is deleted.

2fill in blank

medium

Complete the code to prevent deletion of the referenced object if related objects exist.

Django

from django.db import models

class Category(models.Model):
    name = models.CharField(max_length=100)

class Product(models.Model):
    category = models.ForeignKey(Category, on_delete=models.[1])
    name = models.CharField(max_length=200)

Drag options to blanks, or click blank then click option'

ADO_NOTHING

BCASCADE

CSET_NULL

DPROTECT

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE deletes related objects instead of blocking deletion.

SET_NULL requires nullable fields and does not block deletion.

Using PROTECT stops deletion of a Category if any Product refers to it.

3fill in blank

hard

Fix the error in the code to allow setting the foreign key to null when the referenced object is deleted.

Django

from django.db import models

class Publisher(models.Model):
    name = models.CharField(max_length=100)

class Magazine(models.Model):
    publisher = models.ForeignKey(Publisher, on_delete=models.[1], null=True)
    title = models.CharField(max_length=200)

Drag options to blanks, or click blank then click option'

ASET_NULL

BCASCADE

CPROTECT

DDO_NOTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE deletes the related object instead of setting null.

PROTECT prevents deletion and does not set null.

SET_NULL allows the publisher field to become null when the Publisher is deleted. The field must have null=True.

4fill in blank

hard

Fill both blanks to create a foreign key that sets the field to null on deletion and allows null values.

Django

class Article(models.Model):
    author = models.ForeignKey(User, on_delete=models.[1], [2]=True)
    headline = models.CharField(max_length=255)

Drag options to blanks, or click blank then click option'

ASET_NULL

Bnull

Cblank

DCASCADE

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE deletes the article instead of setting author to null.

Using blank=True does not allow null values in the database.

Use SET_NULL for on_delete and null=True to allow the field to be empty when the related User is deleted.

5fill in blank

hard

Fill all three blanks to define a foreign key that protects deletion, allows blank input, and does not allow null values.

Django

class Comment(models.Model):
    post = models.ForeignKey(Post, on_delete=models.[1], [2]=False, [3]=True)
    content = models.TextField()

Drag options to blanks, or click blank then click option'

APROTECT

Bnull

Cblank

DCASCADE

Attempts:

3 left

💡 Hint

Common Mistakes

Using CASCADE deletes comments when post is deleted.

Setting null=True allows null values which is not desired here.

Use PROTECT to prevent deletion of Post if comments exist, null=False to disallow nulls, and blank=True to allow empty input in forms.