A One-to-One relationship is used when one object of a model corresponds to exactly one object of another model. For example, a table of employees and another table of employee ID badges, where each employee has exactly one unique ID badge. To specify a One-to-One relation, use models.OneToOneField.

id_badge = models.OneToOneField(IdBadge, on_delete=models.CASCADE, related_name=employee).

OneToOneField accepts all of the extra arguments accepted by ForeignKey.

There is just example of usage One-to-One relations. We will not use it in our project.

from django.db import models

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

class Badge(models.Model):
    employee = models.OneToOneField(Employee, on_delete=models.CASCADE, related_name='badge')
    badge_number = models.CharField(max_length=50)
    issue_date = models.DateField()

employee = Employee.objects.get(name='Jane Doe')
employee_badge = employee.badge  # Accessing Badge through Employee instance

badge = Badge.objects.get(badge_number='123456789')
employee = badge.employee  # Accessing Employee from Badge instance

You can learn more about this relation in the official documentation.