Accessing the user's request in a post_save signal

Question

I have done the below post_save signal in my project.

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

# CORE - SIGNALS
# Core Signals will operate based on post

def after_save_handler_attr_audit_obj(sender, **kwargs):
    print User.get_profile()

    if hasattr(kwargs['instance'], 'audit_obj'):
        if kwargs['created']:
            kwargs['instance'].audit_obj.create(operation="INSERT", operation_by=**USER.ID**).save()
        else:
            kwargs['instance'].audit_obj.create(operation="UPDATE").save()


# Connect the handler with the post save signal - Django 1.2
post_save.connect(after_save_handler_attr_audit_obj, dispatch_uid="core.models.audit.new")

The operation_by column, I want to get the user_id and store it. Any idea how can do that?

Answer 1

Can't be done. The current user is only available via the request, which is not available when using purely model functionality. Access the user in the view somehow.

Answer 2

You can do that with the help of middleware. Create get_request.py in your app. Then

from threading import current_thread

from django.utils.deprecation import MiddlewareMixin


_requests = {}


def current_request():
    return _requests.get(current_thread().ident, None)


class RequestMiddleware(MiddlewareMixin):

    def process_request(self, request):
        _requests[current_thread().ident] = request

    def process_response(self, request, response):
        # when response is ready, request should be flushed
        _requests.pop(current_thread().ident, None)
        return response


    def process_exception(self, request, exception):
        # if an exception has happened, request should be flushed too
         _requests.pop(current_thread().ident, None)

Then add this middleware to your settings:

MIDDLEWARE = [
    ....
    '<your_app>.get_request.RequestMiddleware',
]

Then add import to your signals:

from django.db.models.signals import post_save
from django.contrib.auth.models import User
from <your_app>.get_request import current_request

# CORE - SIGNALS
# Core Signals will operate based on post

def after_save_handler_attr_audit_obj(sender, **kwargs):
    print(Current User, current_request().user)
    print User.get_profile()

    if hasattr(kwargs['instance'], 'audit_obj'):
        if kwargs['created']:
            kwargs['instance'].audit_obj.create(operation="INSERT", operation_by=**USER.ID**).save()
        else:
            kwargs['instance'].audit_obj.create(operation="UPDATE").save()


# Connect the handler with the post save signal - Django 1.2
post_save.connect(after_save_handler_attr_audit_obj, dispatch_uid="core.models.audit.new")

Answer 3

I was able to do it by inspecting the stack and looking for the view then looking at the local variables for the view to get the request. It feels like a bit of a hack, but it worked.

import inspect, os

@receiver(post_save, sender=MyModel)
def get_user_in_signal(sender, **kwargs):
    for entry in reversed(inspect.stack()):
        if os.path.dirname(__file__) + '/views.py' == entry[1]:
            try:
                user = entry[0].f_locals['request'].user
            except:
                user = None
            break
    if user:
        # do stuff with the user variable

Answer 4

Ignacio is right. Django's model signals are intended to notify other system components about events associated with instances and their respected data, so I guess it's valid that you cannot, say, access request data from a model post_save signal, unless that request data was stored on or associated with the instance.

I guess there are lots of ways to handle it, ranging from worse to better, but I'd say this is a prime example for creating class-based/function-based generic views that will automatically handle this for you.

Have your views that inherit from CreateView, UpdateView or DeleteView additionally inherit from your AuditMixin class if they handle verbs that operate on models that need to be audited. The AuditMixin can then hook into the views that successfully create\update\delete objects and create an entry in the database.

Makes perfect sense, very clean, easily pluggable and gives birth to happy ponies. Flipside? You'll either have to be on the soon-to-be-released Django 1.3 release or you'll have to spend some time fiddlebending the function-based generic views and providing new ones for each auditing operation.

Answer 5

Why not adding a middleware with something like this :

class RequestMiddleware(object):

    thread_local = threading.local()

    def process_request(self, request):
        RequestMiddleware.thread_local.current_user = request.user

and later in your code (specially in a signal in that topic) :

thread_local = RequestMiddleware.thread_local
if hasattr(thread_local, 'current_user'):
    user = thread_local.current_user
else:
    user = None

Answer 6

For traceability add two attributes to your Model(created_by and updated_by), in "updated_by" save the last user who modified the record. Then in your signal you have the user:

models.py:

class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')
    created_by = models. (max_length=100)
    updated_by = models. (max_length=100)

views.py

    p = Question.objects.get(pk=1)
    p.question_text = 'some new text'
    p.updated_by = request.user
    p.save()

signals.py

@receiver(pre_save, sender=Question)
def do_something(sender, instance, **kwargs):
    try:
        obj = Question.objects.get(pk=instance.pk)
    except sender.DoesNotExist:
        pass
    else:
        if not obj.user == instance.user: # Field has changed
            # do something
            print('change: user, old=%s new=%s' % (obj.user, instance.user))

Answer 7

You could also use django-reversion for this purpose, e.g.

from reversion.signals import post_revision_commit
import reversion

@receiver(post_save)
def post_revision_commit(sender, **kwargs):
    if reversion.is_active():
        print(reversion.get_user())

Read more on their API https://django-reversion.readthedocs.io/en/stable/api.html#revision-api

Answer 8

You can do a small hack by overriding you model save() method and setting the user on the saved instance as additional parameter. To get the user I used get_current_authenticated_user() from django_currentuser.middleware.ThreadLocalUserMiddleware (see https://pypi.org/project/django-currentuser/).

In your models.py:

from django_currentuser.middleware import get_current_authenticated_user

class YourModel(models.Model):
    ...
    ...

    def save(self, *args, **kwargs):
        # Hack to pass the user to post save signal.
        self.current_authenticated_user = get_current_authenticated_user()
        super(YourModel, self).save(*args, **kwargs)

In your signals.py:

@receiver(post_save, sender=YourModel)
def your_model_saved(sender, instance, **kwargs):
    user = getattr(instance, 'current_authenticated_user', None)

PS: Don't forget to add 'django_currentuser.middleware.ThreadLocalUserMiddleware' to your MIDDLEWARE_CLASSES.

Answer 9

I imagine you would have figured this out, but I had the same problem and I realised that all the instances I create had a reference to the user that creates them (which is what you are looking for)

Answer 10

it's possible i guess.

in models.py

class _M(models.Model):
    user = models.ForeignKey(...)

in views.py

def _f(request):
    _M.objects.create(user=request.user)

in signals.py

@receiver(post_save, sender=_M)
def _p(sender, instance, created, **kwargs):
   user = instance.user

No ?

Answer 11

Request object can be obtained from frame record by inspecting.

import inspect

request = [
    frame_record[0].f_locals["request"]
    for frame_record in inspect.stack()
    if frame_record[3] == "get_response"
][0]

Answer 12

def get_requested_user():
    import inspect
    for frame_record in inspect.stack():
        if frame_record[3] == 'get_response':
            request = frame_record[0].f_locals['request']
            return request.user
    else:
        return None

Answer 13

context_processors.py

from django.core.cache import cache

def global_variables(request):
    cache.set('user', request.user)

----------------------------------
in you model

from django.db.models.signals import pre_delete
from django.dispatch import receiver
from django.core.cache import cache
from news.models import News

@receiver(pre_delete, sender=News)
def news_delete(sender, instance, **kwargs):
    user = cache.get('user')

in settings.py

TEMPLATE_CONTEXT_PROCESSORS = (
    'web.context_processors.global_variables',
)