Explain the purpose and use of the OneToOneField in Django ORM.

The OneToOneField in Django ORM is used to create a "one-to-one" relationship between two models. This means that each record in one model corresponds to exactly one record in the related model.

Example of usage:

from django.db import models

class User(models.Model):
    username = models.CharField(max_length=100)

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    bio = models.TextField()

In this example, each User has exactly one Profile. This is convenient when you want to extend the standard user model with additional fields without modifying the user model itself.

on_delete=models.CASCADE means that when the user is deleted, the associated profile will be automatically deleted.