Connecting signal handlers in Django - Mini Project: Build & Apply

Connecting signal handlers in Django

📖 Scenario: You are building a Django app that needs to perform an action automatically whenever a new user is created. Django signals let you run code in response to certain events, like saving a model.

🎯 Goal: Learn how to connect a signal handler function to Django's post_save signal for the User model. This handler will print a message when a new user is created.

📋 What You'll Learn

Create a signal handler function named welcome_new_user that accepts sender, instance, created, and **kwargs parameters.

Connect the welcome_new_user function to Django's post_save signal for the User model.

Ensure the handler only runs when a new user is created (not updated).

Import all necessary modules and models correctly.

💡 Why This Matters

🌍 Real World

Automatically running code when users sign up helps send welcome messages, set up profiles, or log activity without manual steps.

💼 Career

Understanding Django signals is important for backend developers to create clean, event-driven code that reacts to database changes.

1

Import User model and post_save signal

Write import statements to import User from django.contrib.auth.models and post_save from django.db.models.signals.

Django

# Your code here

Need a hint?

Use from django.contrib.auth.models import User and from django.db.models.signals import post_save.

2

Define the signal handler function

Define a function named welcome_new_user that takes parameters sender, instance, created, and **kwargs. Inside the function, add an if statement to check if created is True. If so, write a comment inside the block saying # New user created.

Django

from django.contrib.auth.models import User
from django.db.models.signals import post_save

# Define the signal handler function
# Your code here

Need a hint?

Define the function with the exact name and parameters. Use if created: to check if the user is new.

3

Connect the signal handler to post_save for User

Use post_save.connect to connect the welcome_new_user function to the post_save signal for the User model. Pass sender=User as an argument.

Django

from django.contrib.auth.models import User
from django.db.models.signals import post_save

def welcome_new_user(sender, instance, created, **kwargs):
    if created:
        # New user created

# Connect the signal handler
# Your code here

Need a hint?

Use post_save.connect(welcome_new_user, sender=User) to connect the handler.

4

Add a print statement inside the handler

Inside the if created: block of welcome_new_user, add a print statement that outputs Welcome, {instance.username}! using an f-string.

Django

from django.contrib.auth.models import User
from django.db.models.signals import post_save

def welcome_new_user(sender, instance, created, **kwargs):
    if created:
        # New user created
        # Your code here

post_save.connect(welcome_new_user, sender=User)

Need a hint?

Use print(f"Welcome, {instance.username}!") inside the if created: block.