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Django: Python Web Development Unleashed

One To One Relationship

Explore how to create and manage one to one relationships between Django models using the OneToOneField. Understand field parameters like on_delete and related_name, and see how these relationships appear in the Django admin interface to enforce unique project leadership.

We'll cover the following...

OneToOneField field

This field is used for a One-to-One relationship. To understand how this relationship between models works, we don’t need to add another model. We will use our existing models:

  • Company
  • Employee
  • Projects

Now, the new relationship we are adding is that one project will have only one employee as a Team Lead. Similarly, one employee will be the Team Lead for only one project. This makes it a One-to-One relationship. This relationship is shown in the following illustration:

The implementation of the models will be the following:

Python 3.5
from django.db import models
from datetime import date
# Create your models here.
class Company(models.Model):
    name = models.CharField(max_length=264,unique=True)
    number_of_employees= models.IntegerField(default=0)
    
    def __str__(self):
        return self.name
class Employee(models.Model):
    employee_name = models.CharField(max_length=264, unique= True)
    company_name = models.ForeignKey(Company, on_delete=models.CASCADE)
    date_of_birth = models.DateField(default= date.today)
    def __str__(self):
        return self.employee_name
class Project(models.Model):
    project_name = models.CharField(max_length=264, unique= True)
    employee_name = models.ManyToManyField('Employee')
    team_lead = models.OneToOneField('Employee', on_delete=models.CASCADE, related_name='team_lead')
    def __str__(self):
        return self.project_name

In the ...