Chaining querysets in Django - Mini Project: Build & Apply

Chaining Querysets in Django

📖 Scenario: You are building a simple Django app to manage a bookstore. You want to find books that are either published after 2010 or have more than 500 pages. You will use chaining querysets to combine these two filters.

🎯 Goal: Create two querysets filtering books by different criteria, then chain them together to get a combined list of books matching either condition.

📋 What You'll Learn

Create a Django model Book with fields title (string), published_year (integer), and pages (integer).

Create a queryset recent_books filtering books published after 2010.

Create a queryset long_books filtering books with more than 500 pages.

Chain recent_books and long_books using union() to get combined_books.

💡 Why This Matters

🌍 Real World

Chaining querysets helps combine multiple filters in Django apps, like showing products that meet different criteria in an online store.

💼 Career

Understanding queryset chaining is important for Django developers to write efficient database queries and build flexible data views.

1

Define the Book model

Create a Django model called Book with fields: title as models.CharField(max_length=100), published_year as models.IntegerField(), and pages as models.IntegerField().

Django

# Define the Book model with title, published_year, and pages fields
from django.db import models

# Your code here

Need a hint?

Use models.CharField for text and models.IntegerField for numbers.

2

Create querysets for recent and long books

Create a queryset called recent_books that filters Book objects with published_year greater than 2010. Also create a queryset called long_books that filters Book objects with pages greater than 500.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    published_year = models.IntegerField()
    pages = models.IntegerField()

# Create recent_books queryset filtering published_year > 2010
# Create long_books queryset filtering pages > 500
# Your code here

Need a hint?

Use filter() with __gt to get values greater than a number.

3

Chain the querysets using union()

Create a queryset called combined_books by chaining recent_books and long_books using the union() method.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    published_year = models.IntegerField()
    pages = models.IntegerField()

recent_books = Book.objects.filter(published_year__gt=2010)
long_books = Book.objects.filter(pages__gt=500)

# Chain recent_books and long_books using union() into combined_books
# Your code here

Need a hint?

Use union() to combine two querysets without duplicates.

4

Use combined_books in a view

In a Django view function called book_list, return a context dictionary with key books set to combined_books. Use render() to render a template called books.html with this context.

Django

from django.db import models
from django.shortcuts import render

class Book(models.Model):
    title = models.CharField(max_length=100)
    published_year = models.IntegerField()
    pages = models.IntegerField()

recent_books = Book.objects.filter(published_year__gt=2010)
long_books = Book.objects.filter(pages__gt=500)
combined_books = recent_books.union(long_books)

# Define a view function book_list that renders 'books.html' with context {'books': combined_books}
# Your code here

Need a hint?

Use render(request, template_name, context) to send data to the template.