ForeignKey for one-to-many in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a ForeignKey in Django?

A ForeignKey in Django is a field used to create a one-to-many relationship between two models. It links one model to another by storing the primary key of the related model.

beginner

How do you define a one-to-many relationship using ForeignKey in Django models?

You add a ForeignKey field in the 'many' side model pointing to the 'one' side model. For example, in a Blog and Entry setup, Entry has a ForeignKey to Blog.

intermediate

What does the 'on_delete' parameter do in a ForeignKey field?

The 'on_delete' parameter defines what happens to related objects when the referenced object is deleted. Common options are CASCADE (delete related), SET_NULL (set to null), and PROTECT (prevent deletion).

intermediate

How can you access all related objects from the 'one' side in a one-to-many ForeignKey relationship?

You use the reverse relation manager. By default, Django creates a manager named <modelname>_set. For example, blog.entry_set.all() returns all entries for a blog.

beginner

Why is using ForeignKey better than storing IDs manually for relationships?

ForeignKey ensures data integrity, provides easy querying, and integrates with Django's ORM features like automatic joins and reverse lookups, making code cleaner and safer.

In Django, which model should have the ForeignKey field in a one-to-many relationship?

A The model on the 'many' side

B The model on the 'one' side

C Both models

D Neither model

The ForeignKey is placed on the 'many' side model to link it to the 'one' side model.

What does the 'on_delete=models.CASCADE' option do in a ForeignKey?

A Prevents deletion of the referenced object

B Deletes related objects when the referenced object is deleted

C Sets the ForeignKey to null on deletion

D Does nothing on deletion

CASCADE deletes all related objects automatically when the referenced object is deleted.

How do you access all related objects from the 'one' side in a ForeignKey relationship?

A You cannot access related objects from the 'one' side

B Using ForeignKey field directly

C Using <modelname>_set manager

D Using a separate query unrelated to ForeignKey

Django automatically creates a reverse manager named _set to access related objects.

Which of these is NOT a valid 'on_delete' option in Django ForeignKey?

A IGNORE

B CASCADE

C PROTECT

D SET_NULL

'IGNORE' is not a valid on_delete option in Django.

Why is using ForeignKey preferred over manually storing IDs for relationships?

A It requires more manual code

B It makes the database slower

C It disables reverse lookups

D It ensures data integrity and easier querying

ForeignKey helps maintain data integrity and provides easy querying and reverse lookups.

Explain how to create a one-to-many relationship using ForeignKey in Django models.

Think about which model holds the ForeignKey and what happens on deletion.

Describe how to access related objects from the 'one' side in a ForeignKey relationship in Django.

Remember Django creates a manager automatically for reverse lookups.