Field lookups (exact, contains, gt, lt) in Django - Mini Project: Build & Apply

Filtering Django QuerySets with Field Lookups

📖 Scenario: You are building a simple Django app to manage a bookstore's inventory. You want to filter books based on different criteria like exact title, partial author name, price greater than a value, and publication year less than a value.

🎯 Goal: Learn how to use Django ORM field lookups exact, contains, gt, and lt to filter QuerySets.

📋 What You'll Learn

Create a Django model Book with fields title, author, price, and year_published

Create a QuerySet variable books with some sample book objects

Create a variable price_threshold set to 20

Filter books with exact title 'Django Basics' using exact lookup

Filter books with author name containing 'Smith' using contains lookup

Filter books with price greater than price_threshold using gt lookup

Filter books published before year 2010 using lt lookup

💡 Why This Matters

🌍 Real World

Filtering data in Django apps is essential for showing users only relevant information, like books matching their search criteria.

💼 Career

Understanding Django ORM field lookups is a key skill for backend developers working with Django to build efficient and readable database queries.

1

Create the Book model and sample data

Create a Django model class called Book with fields title (CharField), author (CharField), price (FloatField), and year_published (IntegerField). Then create a QuerySet variable called books with these exact book instances: Book(title='Django Basics', author='John Smith', price=15.99, year_published=2015), Book(title='Advanced Django', author='Jane Doe', price=25.50, year_published=2018), Book(title='Python 101', author='Mike Smith', price=19.99, year_published=2008), Book(title='Web Development', author='Anna Johnson', price=22.00, year_published=2005).

Django

# Define the Book model and create the books QuerySet
# Your code here

Need a hint?

Use Django model fields like CharField for text, FloatField for price, and IntegerField for year. Create a list of Book instances for books.

2

Set the price threshold variable

Create a variable called price_threshold and set it to the float value 20.0.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)
    price = models.FloatField()
    year_published = models.IntegerField()

books = [
    Book(title='Django Basics', author='John Smith', price=15.99, year_published=2015),
    Book(title='Advanced Django', author='Jane Doe', price=25.50, year_published=2018),
    Book(title='Python 101', author='Mike Smith', price=19.99, year_published=2008),
    Book(title='Web Development', author='Anna Johnson', price=22.00, year_published=2005),
]

# Create price_threshold variable
# Your code here

Need a hint?

Just create a variable named price_threshold and assign it the value 20.0.

3

Filter books using field lookups

Create four new variables to filter the books list using Django-like field lookups: exact_title for books with title exactly 'Django Basics' using exact lookup, author_contains_smith for books with author containing 'Smith' using contains lookup, price_gt_threshold for books with price greater than price_threshold using gt lookup, and year_lt_2010 for books published before 2010 using lt lookup. Use list comprehensions to simulate these filters.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)
    price = models.FloatField()
    year_published = models.IntegerField()

books = [
    Book(title='Django Basics', author='John Smith', price=15.99, year_published=2015),
    Book(title='Advanced Django', author='Jane Doe', price=25.50, year_published=2018),
    Book(title='Python 101', author='Mike Smith', price=19.99, year_published=2008),
    Book(title='Web Development', author='Anna Johnson', price=22.00, year_published=2005),
]

price_threshold = 20.0

# Filter books using exact, contains, gt, lt lookups
# Your code here

Need a hint?

Use list comprehensions with conditions matching the field lookups: == for exact, in for contains, > for gt, and < for lt.

4

Complete the filtering with Django QuerySet style

Add a final line that creates a Django QuerySet-like filter call named filtered_books that chains all four filters using Django ORM syntax: filter books with title exactly 'Django Basics', author containing 'Smith', price greater than price_threshold, and year published less than 2010. Use the Django QuerySet filter() method with keyword arguments and chaining.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)
    price = models.FloatField()
    year_published = models.IntegerField()

books = [
    Book(title='Django Basics', author='John Smith', price=15.99, year_published=2015),
    Book(title='Advanced Django', author='Jane Doe', price=25.50, year_published=2018),
    Book(title='Python 101', author='Mike Smith', price=19.99, year_published=2008),
    Book(title='Web Development', author='Anna Johnson', price=22.00, year_published=2005),
]

price_threshold = 20.0

exact_title = [book for book in books if book.title == 'Django Basics']
author_contains_smith = [book for book in books if 'Smith' in book.author]
price_gt_threshold = [book for book in books if book.price > price_threshold]
year_lt_2010 = [book for book in books if book.year_published < 2010]

# Create filtered_books using Django ORM filter chaining
# Your code here

Need a hint?

Use Django ORM chaining with filter() and double underscores for lookups like title__exact, author__contains, price__gt, and year_published__lt.