Creating and Managing Relationships in Databases with Django ORM
Creating and managing relationships in databases using Django ORM (Object-Relational Mapping) is a core part of building any Django application. Django makes it intuitive and easy to define relationships using Python classes.
🔗 Types of Relationships in Django ORM
Django supports the following relationship types:
One-to-One (OneToOneField)
One-to-Many (ForeignKey)
Many-to-Many (ManyToManyField)
🧱 1. One-to-One Relationship
Used when each row in one table is linked to one and only one row in another table.
✅ Example:
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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()
Each Profile is linked to exactly one User.
🔁 2. One-to-Many Relationship (ForeignKey)
This is the most common relationship. One record in the parent table can relate to multiple records in the child table.
✅ Example:
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class Author(models.Model):
name = models.CharField(max_length=100)
class Book(models.Model):
title = models.CharField(max_length=200)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
An Author can have many Books.
🧪 Accessing Data:
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author = Author.objects.get(id=1)
books = author.book_set.all() # get all books by this author
🔄 3. Many-to-Many Relationship
Used when multiple records in one model can be related to multiple records in another model.
✅ Example:
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class Student(models.Model):
name = models.CharField(max_length=100)
class Course(models.Model):
title = models.CharField(max_length=100)
students = models.ManyToManyField(Student)
A Student can enroll in many Courses, and a Course can have many Students.
🧪 Accessing Data:
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student = Student.objects.get(id=1)
student_courses = student.course_set.all()
course = Course.objects.get(id=1)
course_students = course.students.all()
🛠️ Managing Relationships in Views/Forms
Create a Related Object:
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# Creating a book for an author
author = Author.objects.get(id=1)
Book.objects.create(title="New Book", author=author)
Add to Many-to-Many:
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student = Student.objects.get(id=1)
course = Course.objects.get(id=2)
student.course_set.add(course)
🔧 Using Related Name
You can customize the reverse relation name using related_name.
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class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name="books")
# Usage:
author.books.all()
🔍 Querying Across Relationships
Example:
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# Get all books by authors named "John"
Book.objects.filter(author__name="John")
# Get all students in a course titled "Math"
Student.objects.filter(course__title="Math")
✅ Summary Table
Relationship Type Field Used Example Use
One-to-One OneToOneField User and Profile
One-to-Many ForeignKey Author and Book
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