How to Use and Create Signals in Django?

Hi Dev,

In this comprehensive tutorial, you will learn how to use and create signals in Django. We'll explore how to automatically trigger actions like creating a profile when a new user is registered, using built-in signals like post_save, pre_save, and more.

This article gives you a complete guide with a working example of Django custom signals, including models, forms, views, and signals. Let's get started with Django signals step-by-step.

Django signals are used to perform actions after or before a model’s instance is saved or deleted. For example, creating a user profile immediately after a user is registered.

Types of Django Signals:

• pre_save/post_save: Triggered before/after save() method is called.
• pre_delete/post_delete: Triggered before/after delete() method is called.
• pre_init/post_init: Triggered before/after the model’s __init__() constructor is run.

We’ll now walk through a real-world example using the post_save signal to automatically create a user profile.

django-admin startproject example

python3 manage.py startapp core

....
INSTALLED_APPS = [
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'core',
]

from django.db import models
from django.contrib.auth.models import User
from PIL import Image

class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
image = models.ImageField(default='default.jpg', upload_to='profile_pics')

def __str__(self):
    return f'{self.user.username} Profile'

python manage.py makemigrations
python manage.py migrate

from django import forms
from django.contrib.auth.models import User
from django.contrib.auth.forms import UserCreationForm
from .models import Profile

class UserRegisterForm(UserCreationForm):
email = forms.EmailField()

class Meta:
    model = User
    fields = ['username', 'email', 'password1', 'password2']


class UserUpdateForm(forms.ModelForm):
email = forms.EmailField()

class Meta:
    model = User
    fields = ['username', 'email']


class ProfileUpdateForm(forms.ModelForm):
class Meta:
    model = Profile
    fields = ['image']

from django.shortcuts import render, redirect
from django.contrib import messages
from django.contrib.auth.decorators import login_required
from .forms import UserRegisterForm, UserUpdateForm, ProfileUpdateForm

def register(request):
if request.method == 'POST':
    form = UserRegisterForm(request.POST)
    if form.is_valid():
        form.save()
        username = form.cleaned_data.get('username')
        messages.success(request, f'Your account has been created! You can now log in.')
        return redirect('login')
else:
    form = UserRegisterForm()
return render(request, 'users/register.html', {'form': form})


@login_required
def profile(request):
if request.method == 'POST':
    u_form = UserUpdateForm(request.POST, instance=request.user)
    p_form = ProfileUpdateForm(request.POST, request.FILES, instance=request.user.profile)
    if u_form.is_valid() and p_form.is_valid():
        u_form.save()
        p_form.save()
        messages.success(request, f'Your profile has been updated!')
        return redirect('profile')
else:
    u_form = UserUpdateForm(instance=request.user)
    p_form = ProfileUpdateForm(instance=request.user.profile)

context = {
    'u_form': u_form,
    'p_form': p_form
}

return render(request, 'users/profile.html', context)

from django.db.models.signals import post_save
from django.contrib.auth.models import User
from django.dispatch import receiver
from .models import Profile

@receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
if created:
    Profile.objects.create(user=instance)

@receiver(post_save, sender=User)
def save_profile(sender, instance, **kwargs):
instance.profile.save()

This ensures that a Profile is automatically created whenever a new User is added to the system.

from django.apps import AppConfig

class CoreConfig(AppConfig):
name = 'core'

def ready(self):
    import core.signals

pre_save Example:

@receiver(pre_save, sender=User)
def checker(sender, instance, **kwargs):
if instance.id:
    current = instance
    previous = User.objects.get(id=instance.id)
    if previous.reaction != current.reaction:
        # save method will continue

Connecting Signals Manually:

post_save.connect(my_function_post_save, sender=MyModel)
pre_save.connect(my_function, sender=User)

I hope this guide helps you implement Django signals successfully in your project!

Happy Coding!