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!