Source: 📖 Django for Professionals ch11 p166

Creating a foreign key link in Django

We'll start with a Book model to represent books on our site:

# models.py

from django.db import models


class Book(models.Model):
	title= models.CharField(max_length=200)
	author = models.CharField(max_length=200)
	

Now suppose we want to add a Review model, so that users can leave reviews for the books they read. This requires a foreign key relation from our Review model to our Book model.

# models.py

...

class Book(models.Model):
	...
	

class Review(models.Model):
	book = models.ForeignKey(
		Book,
		on_delete=models.CASCADE,
		related_name='reviews'
	)
	review_text = models.CharField(max_length=255)

We create a book attribute inside the Review class and assign it to models.ForeignKey, which defaults to a one-to-many relationship. It is standard practice to name this attribute the same as the model to which it is linking.

The first argument we pass to the FogerignKey function is the model to which we are linking, Book. We then assign the CASCADE behaviour on deletion, meaning that if the Book entry to which the review belongs is deleted, so will the review be deleted. Finally we create a related_name attribute, which assigns the name by which we can look up related items in a Book instance — for example, if we had a book object my_book, calling my_book.reviews would return all reviews linked to this instance.