Primary key behavior in Django - Mini Project: Build & Apply

Primary key behavior

📖 Scenario: You are building a simple Django app to manage a list of books in a library. Each book needs a unique identifier so you can find it easily.

🎯 Goal: Create a Django model called Book with a primary key field and a title field. Understand how Django automatically creates a primary key if you don't specify one, and how to define your own primary key.

📋 What You'll Learn

Create a Django model named Book with a title field

Understand Django's default primary key behavior

Add a custom primary key field named isbn as a CharField

Use the primary_key=True attribute on the isbn field

💡 Why This Matters

🌍 Real World

Managing unique identifiers for records in a database is essential in real-world apps like libraries, stores, or user management.

💼 Career

Understanding primary keys is fundamental for backend developers working with databases and Django models.

1

Create the Book model with a title field

Create a Django model class called Book with a title field of type CharField with max length 100.

Django

from django.db import models

# Define the Book model

# Your code here

Need a hint?

Use class Book(models.Model): and add title = models.CharField(max_length=100) inside.

2

Add a custom primary key field named isbn

Add a field called isbn to the Book model as a CharField with max length 13 and set primary_key=True.

Django

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    # Add isbn field as primary key below
    # Your code here

Need a hint?

Define isbn = models.CharField(max_length=13, primary_key=True) inside the Book class.

3

Explain Django default primary key behavior

Add a comment above the Book class explaining that Django automatically adds an id field as primary key if none is specified.

Django

# Your comment here
from django.db import models

class Book(models.Model):
    isbn = models.CharField(max_length=13, primary_key=True)
    title = models.CharField(max_length=100)

Need a hint?

Write a comment starting with # Django automatically adds an 'id' field above the class.

4

Add __str__ method to display book title

Add a __str__ method to the Book model that returns the title field.

Django

# Django automatically adds an 'id' field as primary key if no primary key is defined
from django.db import models

class Book(models.Model):
    isbn = models.CharField(max_length=13, primary_key=True)
    title = models.CharField(max_length=100)

    # Add __str__ method below
    # Your code here

Need a hint?

Define def __str__(self): and return self.title inside it.