I want to execute some code in a Django model when it is first created. After that whenever it is saved I want to execute some other code. The second task can be easily done by overriding the save() method.
How can I do the first task?
Extending sdolan's answer by using receiver decorator:
from django.db import models
from django.dispatch import receiver
class MyModel(models.Model):
pass
#receiver(models.signals.post_save, sender=MyModel)
def execute_after_save(sender, instance, created, *args, **kwargs):
if created:
# code
You can use django signals' post_save:
# models.py
from django.db.models import signals
class MyModel(models.Model):
pass
def my_model_post_save(sender, instance, created, *args, **kwargs):
"""Argument explanation:
sender - The model class. (MyModel)
instance - The actual instance being saved.
created - Boolean; True if a new record was created.
*args, **kwargs - Capture the unneeded `raw` and `using`(1.3) arguments.
"""
if created:
# your code goes here
# django 1.3+
from django.dispatch import dispatcher
dispatcher.connect(my_model_post_save, signal=signals.post_save, sender=MyModel)
# django <1.3
from django.db.models.signals import post_save
post_save.connect(my_model_post_save, sender=MyModel)
field.default
The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.
So, we can use any field callable to do what we want on creation, huh? ;-)
Related
My User has 2 objects.
1. admin - super admin
2. tom - user
MyModel with
class MyModel:
project_user = models.ManyToManyField(User)
Let's suppose tom is creating a MyModel object:
MyModel(project_user=request.user).save()
Here I would like to add admin user automatically to the project_user object when someone creates an object. What will the more efficient way to implement it,How about using signals or def save(self)?
I would recommend using Signals.
from django.contrib.auth.models import User
from django.db.models.signals import post_save
from django.dispatch import receiver
#receiver(post_save, sender=User)
def create_user_profile(sender, instance, created, **kwargs):
if created:
Profile.objects.create(user=instance)
In the snippet above, I'm trying to create a custom model (i.e. Profile) when a default user once created.
Therefore, I think you could write like this:
from django.contrib.auth.models import User
from django.db.models.signals import post_save
from django.dispatch import receiver
#receiver(post_save, sender=MyModel)
def create_user(sender, instance, created, **kwargs):
if created:
User.objects.create_user(username=instance.username)
And create_user() is a helper function of Django.
Edit: Added what I import in the snippet.
I'm struggling with the following.
I'm trying to create a custom signal that will trigger when the current time will be equal to the value of my model's notify_on DateTimeField.
Something like this:
class Notification(models.Model):
...
notify_on = models.DateTimeField()
def send_email(*args, **kwargs):
# send email
signals.when_its_time.connect(send_email, sender=User)
After I've read through all docs and I found no information on how to implement such a signal.
Any ideas?
UPDATE:
Less naive approach with ability to discard irrelevant tasks: https://stackoverflow.com/a/55337663/9631956
Ok, thanks to comments by #SergeyPugach I've done the following:
Added a post_save signal that calls a function that adds a task to the celery. apply_async let's you pass eta - estimated time of arrival which can accept DateTimeField directly, that's very convenient.
# models.py
from django.db.models import signals
from django.db import models
from .tasks import send_notification
class Notification(models.Model):
...
notify_on = models.DateTimeField()
def notification_post_save(instance, *args, **kwargs):
send_notification.apply_async((instance,), eta=instance.notify_on)
signals.post_save.connect(notification_post_save, sender=Notification)
And the actual task in the tasks.py
import logging
from user_api.celery import app
from django.core.mail import send_mail
from django.template.loader import render_to_string
#app.task
def send_notification(self, instance):
try:
mail_subject = 'Your notification.'
message = render_to_string('notify.html', {
'title': instance.title,
'content': instance.content
})
send_mail(mail_subject, message, recipient_list=[instance.user.email], from_email=None)
except instance.DoesNotExist:
logging.warning("Notification does not exist anymore")
I will not get into details of setting up celery, there's plenty of information out there.
Now I will try to figure out how to update the task after it's notification instance was updated, but that's a completely different story.
In django's documentation there is two interesting signals that may help you on this task: pre_save and post_save.
It depends on your needs, but let's say you want to check if your model's notify_on is equal to the current date after saving your model (actually after calling the save() or create() method). If it's your case you can do:
from datetime import datetime
from django.contrib.auth.models import User
from django.db import models
from django.dispatch import receiver
from django.db.models.signals import post_save
class Notification(models.Model):
...
# Every notification is related to a user
# It depends on your model, but i guess you're doing something similar
user = models.ForeignKey(User, related_name='notify', on_delete=models.DO_NOTHING)
notify_on = models.DateTimeField()
...
def send_email(self, *args, **kwargs):
"""A model method to send email notification"""
...
#receiver(post_save, sender=User)
def create_notification(sender, instance, created, **kwargs):
# check if the user instance is created
if created:
obj = Notification.objects.create(user=instance, date=datetime.now().date())
if obj.notify_on == datetime.now().date():
obj.send_email()
And you should know, that django signals won't work by they own only if there is an action that triggers them. What this mean is that Django signals won't loop over your model's instances and perform an operation, but django signals will trigger when your application is performing an action on the model connected to a signal.
Bonus: To perform a loop over your instances and process an action regulary you may need an asyncworker with a Queue database (mostly, Celery with Redis or RabbitMQ).
I want to call a method after this object (in this example Question) is saved.
This is what I got:
class Question(models.Model):
...
def after_save(sender, instance, *args, **kwargs):
some_method(instance)
post_save.connect(Question.after_save, sender=Question)
It kind of works. But the problem is that the instance data is the old one (same as before the save). So some_method(instance) gets the old instance.
But I need the instance with the new data.
The method you call from post_save signal should be outside of the Model. You can put the method inside the models.py or in another file such as signals.py
class Question(models.Model):
...
def some_method(self):
return "hello"
def question_saved(sender, instance, *args, **kwargs):
instance.some_method()
post_save.connect(question_saved, sender=Question)
You can override save method, and call what ever you want after the object gets saved
Here is a related link: Django. Override save for model
What you want is something called signals: https://docs.djangoproject.com/en/3.2/topics/signals/.
Some operations send a signals before and after they're completed successfully. In the docs you can find a list of built-in signals. You can also create custom signals. For example assume that I want to do something specific each time a new user is created. Then my code would be something like this:
users/models.py
from django.contrib.auth.models import AbstractUser
from django.dispatch import receiver
from django.db.models.signals import post_save
class CustomUser(AbstractUser):
pass
###############
# Recieve the signals and get the signals that are sent
# after models are saved and whose sender is CustomUser
###############
#receiver(post_save, sender='CustomUser')
def do_something():
do_something_specific
You can also save your signals in a separate file called signals.py but you need to change your app's apps:
<appname>/apps.py
from django.apps import AppConfig
class AppnameConfig(AppConfig):
name = <appname>
def ready(self):
import <appname>.signals
I'm trying to setup a signal so that when a valid form is saved, a function is ran to carry out a related task.
My app structure is as follows;
- events
- helpers
- __init__.py
- status.py
- models
- signals
- __init__.py
- event.py
- __init__.py
- event.py
- status.py
- views
- __init__.py
- event.py
I believe signals need to be imported as early as possible, before models, so at the top of models/__init__.py I've got from .signals import *.
# views/event.py
class AddEventView(CreateView):
"""
View for adding an Event.
"""
model = Event
form_class = EventForm
success_url = reverse_lazy('events:all_events')
def form_valid(self, form):
self.object = form.save()
signals.event_status.send(
sender=None, request=self.request, event=self.object, status=None
) # Should the sender be self.object?
return super(AddEventView, self).form_valid(form)
# signals/event.py
from django.dispatch import Signal
event_status = Signal(providing_args=["request", "event", "status"])
# helpers/status.py
from ..models import Status, StatusHistory
from ..models.signals import event_status
def create_status(sender, **kwargs):
"""
Create a status for a given event.
"""
event = kwargs['event']
status = kwargs['status']
creator = User.objects.get(pk=event.creator)
try:
current_status = StatusHistory.objects.filter(
event=event).order_by('timestamp')[0]
except IndexError:
# Not sure what we're doing here yet.
pass
if not status:
status = Status.objects.get(description=_("Submitted"))
statushistory = StatusHistory.create(
event=event,
event_status=status,
user=creator
)
statushistory.save()
event_status.connect(create_status)
I'm running the debug server in Pycharm with a break point in the create_status() function & it's never getting hit.
Have I implemented this wrong?
I've used signals in some of my projects and I allways import the signals in the __init__.py of my Django APP (Same folder as settings.py, views.py, urls.py...)
__init__.py:
import signals
signals.py:
from django.db.models.signals import post_save, pre_delete
from django.dispatch import receiver
from my_project.models import *
#receiver(post_save, sender=Modelname) # Called after an object is saved
def create_modelname(sender, **kwargs):
obj = kwargs['instance'] # I get the object being saved here
# ... Here I do whatever I want
#receiver(pre_delete, sender=Modelname) # Called before an object is deleted
def delete_modelname(sender, **kwargs):
obj = kwargs['instance']
# ... Do whatever you need
Remember this 2 imports:
from django.db.models.signals import post_save, pre_delete
from django.dispatch import receiver
Remember to import the signals
To import the signals you need to add import signals in your __init__.py of your project
Using this code, this functions are called automatically by Django when an object of the class Modelname is created or deleted.
The receiver for created object is called after the object is created, and the receiver for deleted object is called before the object is deleted.
I think maybe you just need to import your helpers/status.py eg in models/__init__.py
otherwise your event_status signal gets defined ok but the signal handler create_status never gets connected by Django
if you only have one handler for that signal it might make sense to put it in the same module as the signal definition
I found one case that signal is not working.
Here are cases that signal(pre_save, post_save) won't happen.
Model.objects.filter(pk=pk).update(key=value)
Bulk model functions won't happen signals.
I'm trying to override the default User model in Django to add some logic into the save() method. I'm having a hard time trying to figure out out to go about this.
I'm using Django 1.1 if that helps.
I used post_save since i need to add the user into ldap.. I just added this into a models.py
from django.db import models
from django.contrib.auth.models import User
from django.db.models import signals
from django.dispatch import dispatcher
def user_post_save(sender, instance, **kwargs):
print "got here"
models.signals.post_save.connect(user_post_save, sender=User)
Don't. Instead catch the pre_save signal.
You'd better use a Proxy model, so to use the same table but overriding behavior.
This is the standard way to extend Django's own models, because they cannot be made abstract.
So declare your model as:
from django.contrib.auth.models import User
class CustomUser(User):
class Meta:
proxy = True
def save(self, *args, **kwargs):
# do anything you need before saving
super(CustomUser, self).save(*args, **kwargs)
# do anything you need after saving
and you are done.