1. Introduction

In this tutorial, we'll explore how to create relationships between Django models. We will cover the three types of relationships: One-to-One, One-to-Many, and Many-to-Many.

What you will learn:
- Understanding Django model relationships
- How to create One-to-One relationships
- How to create One-to-Many relationships
- How to create Many-to-Many relationships

Prerequisites:
- Basic understanding of Python
- Knowledge of Django basics
- Django installed on your system

2. Step-by-Step Guide

Django allows you to define relationships between models in three ways: One-to-One, One-to-Many, and Many-to-Many.

• One-to-One: For each record in the parent table, there is one and only one record in the child table.
• One-to-Many: For each record in the parent table, there can be multiple records in the child table.
• Many-to-Many: Records in the parent table can relate to multiple records in the child table and vice versa.

3. Code Examples

3.1 One-to-One Relationship

In Django, a One-to-One relationship can be defined using OneToOneField.

from django.db import models

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

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

In the example above, we've created a One-to-One relationship between User and Profile. Each User can have one Profile, and each Profile is related to one User.

3.2 One-to-Many Relationship

In Django, a One-to-Many relationship can be created using ForeignKey.

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.CASCADE)

In this example, we've created a One-to-Many relationship between Author and Book. An Author can write multiple Books, but each Book has one Author.

3.3 Many-to-Many Relationship

In Django, a Many-to-Many relationship is created using ManyToManyField.

from django.db import models

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

class Course(models.Model):
    name = models.CharField(max_length=100)
    students = models.ManyToManyField(Student)

In this example, we've created a Many-to-Many relationship between Student and Course. A Student can enroll in multiple Courses, and a Course can have multiple Students.

4. Summary

We learned how to create One-to-One, One-to-Many, and Many-to-Many relationships in Django. These relationships allow us to create complex database schemas to represent real-world relationships between entities.

5. Practice Exercises

Exercise 1: Create a One-to-One relationship between Person and License. Each Person can have one License, and each License belongs to one Person.

Exercise 2: Create a One-to-Many relationship between Teacher and Student. A Teacher can have multiple Students, but each Student has one Teacher.

Exercise 3: Create a Many-to-Many relationship between Actor and Movie. An Actor can be in multiple Movies, and a Movie can have multiple Actors.

Solutions

1. One-to-One relationship between Person and License.

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

class License(models.Model):
    number = models.CharField(max_length=15)
    person = models.OneToOneField(Person, on_delete=models.CASCADE)

1. One-to-Many relationship between Teacher and Student.

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

class Student(models.Model):
    name = models.CharField(max_length=100)
    teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE)

1. Many-to-Many relationship between Actor and Movie.

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

class Movie(models.Model):
    title = models.CharField(max_length=100)
    actors = models.ManyToManyField(Actor)

Continue your learning by exploring different types of relationships and how they can be used in more complex models.