? Model Relationships in Django

? Quick Overview

Django model relationships allow you to connect data across multiple models using relational fields. The three core relationship fields are OneToOneField, ForeignKey, and ManyToManyField.

? Key Concepts

• One-to-one relationships
• Many-to-one relationships
• Many-to-many relationships

? Syntax & Theory

Django provides specialized fields to define relationships directly in model definitions. These fields manage joins, constraints, and reverse lookups automatically.

? OneToOneField

# Each user has exactly one profile
from django.db import models
class Profile(models.Model):
user = models.OneToOneField('auth.User', on_delete=models.CASCADE)
bio = models.TextField()

? ForeignKey

# Multiple books can belong to one author
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)

? ManyToManyField

# Students can enroll in multiple courses
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)

? Explanation

• OneToOneField creates a strict one-to-one mapping.
• ForeignKey enables many-to-one relationships.
• ManyToManyField supports flexible many-to-many links.

? Use Cases

• User profiles linked to accounts
• Blogs with multiple posts per author
• Students enrolling in courses