Relationship query patterns in Django - Mini Project: Build & Apply

Relationship Query Patterns in Django

📖 Scenario: You are building a simple library system. There are Authors and Books. Each book is written by one author. You want to practice how to query related data using Django's ORM.

🎯 Goal: Create Django models for Author and Book with a relationship. Then write queries to find all books by a specific author and all authors who have written books.

📋 What You'll Learn

Create a Django model Author with a name field

Create a Django model Book with a title field and a foreign key to Author

Write a query to get all books by the author named 'Jane Austen'

Write a query to get all authors who have written at least one book

💡 Why This Matters

🌍 Real World

Managing related data is common in web apps like libraries, blogs, or stores. Knowing how to query related models helps you build powerful features.

💼 Career

Django developers often work with related models. Mastering relationship queries is essential for backend development and data handling.

1

Create Author and Book models

Create a Django model called Author with a name field as models.CharField(max_length=100). Also create a model called Book with a title field as models.CharField(max_length=200) and a foreign key called author to Author using models.ForeignKey(Author, on_delete=models.CASCADE).

Django

# Define Author and Book models here
# Your code here

Need a hint?

Remember to import models from django.db. Use models.CharField for text fields and models.ForeignKey for relationships.

2

Set author name to query

Create a variable called author_name and set it to the string 'Jane Austen'. This will be used to find books by this author.

Django

from django.db import models

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)

# Set the author name to query
# Your code here

Need a hint?

Just create a variable author_name and assign the exact string 'Jane Austen'.

3

Query books by author name

Write a Django ORM query to get all Book objects where the related author's name matches the variable author_name. Assign the result to a variable called books_by_author.

Django

from django.db import models

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)

author_name = 'Jane Austen'

# Query books by author name
# Your code here

Need a hint?

Use double underscores author__name to filter books by the author's name.

4

Query authors with books

Write a Django ORM query to get all Author objects who have written at least one book. Assign the result to a variable called authors_with_books. Use distinct() to avoid duplicates.

Django

from django.db import models

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)

author_name = 'Jane Austen'

books_by_author = Book.objects.filter(author__name=author_name)

# Query authors who have written books
# Your code here

Need a hint?

Use book__isnull=False to find authors with books and add distinct() to avoid duplicates.