Django two same signal types - django

Question

I don't understand how 2 signals executed together relate to each other. For example consider the following:
from django.db import models
from django.contrib.auth.models import User
from PIL import Image
from django.db.models.signals import post_save
from django.dispatch import receiver
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'
# Overriding save method-image resizing
def save(self, **kwargs):
super().save(kwargs)
img = Image.open(self.image.path)
if img.height > 300 or img.width > 300:
output_size = (300, 300)
img.thumbnail(output_size)
img.save(self.image.path) # save() of parent class
#Signals when a user is registered his profile is automatically updated
#receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
if created:
Profile(user=instance) #could do Profile.objects.create(user=instance) instead to replace the 2 lines
instance.profile.save() #reverse query
I understand the following:
create_profile: is my receiver function. It will do something when .save() method takes place, in our case will create a Profile instance and save it.
sender: is the Model that is actually signalling this to take place. So in our case, if we want a signal to take place when the save method is executed on User model then the sender would be the User.
post_save is the signal
Regarding my question now. I have seen the above function broken down into the two following functions.
#receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs):
if created:
Profile(user=instance)
#receiver(post_save, sender=User)
def save_profile(sender, instance, **kwargs):
instance.profile.save() #reverse query
I am aware it is pointless since I could do what I did but I don't understand how does my save_profile function 'remembers' the Profile instance made on create_profile?
As far as I can tell, save_profile is a separate function that has no reference to create_profile function (example by create_profile or so on the save_profile body).
I am assuming when a user instance is saved the create_profile function is executed it makes a profile object then the save_profile function is executed and for same user instance the profile object is saved,
but I still don't understand how it knows I refer to same profile made by that instance.

Answer 1

Why you not state it is example from Corey tutorial ?
Corey Tutorial, part 8, and if I not mistaken he didnt have to create two separate signals, because one was enough ..
To your question:
The functions are:
#receiver(post_save, sender=User)
def create_profile_handler(sender, instance, created, **kwargs):
#Run each time a new user is created, and attach to the user a profile !
# sender - The model class (User)
# instance - The actual instance being saved. (User)
# created - A boolean. 'True' if a new record was created.
if created:
Profile.objects.create(user=instance)
#'create' - initialize and save a profile and attach it to the User
# Now, lets save the profile each time the user object is been saved.
#receiver(post_save, sender=User)
def save_profile_handler(sender, instance, **kwargs):
instance.profile.save() # User.profile.save() - saves the profile
we know from the Django Docs, that create() method include save() operation in it.
So not only that the second signal is redundant (because we can do its operations in the first signal), further more - the save is a bit redundant it self (because create calls save).