Cascade for ForeignKey and OneToOneField

Description

This check ensures that ForeignKey and OneToOneField fields are using the CASCADE option for the on_delete parameter.

Rationale

Using CASCADE for the on_delete parameter in ForeignKey and OneToOneField fields ensures that related objects are automatically deleted when the referenced object is deleted, helping maintain database integrity. Other options, like PROTECT, SET_NULL, or SET_DEFAULT, may be appropriate in some cases, but using CASCADE is a safer default choice.

Example

Consider the following model:

from django.db import models

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

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.PROTECT)

The author field is a ForeignKey field, but it's not using the CASCADE option for on_delete. The check would detect this and recommend changing the on_delete option to models.CASCADE:

author = models.ForeignKey(Author, on_delete=models.CASCADE)

However, if you have a specific reason for not using CASCADE, you should evaluate the impact on your application's data integrity and adjust the check accordingly.