request.user returns a SimpleLazyObject, how do I "wake" it?

Question

I have the following method:

def _attempt(actor):
    if actor.__class__ != User:
        raise TypeError

Which is called from a view:

self.object.attempt(self.request.user)

As you can see, the _attempt method expects actor to be type django.contrib.auth.models.User, however the object appears to be of type django.utils.functional.SimpleLazyObject. Why is this so? And more importantly, how can I convert the LazyObject (which apparently is a kind of wrapper for a User object) into a User object?

More info on Request.user is available here: https://docs.djangoproject.com/en/dev/ref/request-response/#django.http.HttpRequest.user This documentation seems to indicate the request.user should be a User object...

======Post-edit=====

I've got the following method now:

def _attempt(obj, action, actor, msg): 
    actor.is_authenticated() 
    if isinstance(actor, LazyObject): 
        print type(actor) 

I'm passing a user, however the if condition is still true, actor is still a LazyObject. Why is this so?

Selfdeceit

Answer 1

See my answer on a similar question.

Django lazy loads request.user so that it can be either User or AnonymousUser depending on the authentication state. It only "wakes up" and returns the appropriate class when an attribute is accessed on it. Unfortunately, __class__ doesn't count because that's a primitive class attribute. There's occasions where you might need to know that this is actually a SimpleLazyObject type, and therefore it would be wrong to proxy it on to User or AnonymousUser.

Long and short, you simply can't do this comparison as you have it. But, what are you really trying to achieve here? If you're trying to check if it's a User or AnonymousUser, there's request.user.is_authenticated() for that, for example.

As a general rule though, you shouldn't abuse duck typing. A parameter should always be a particularly type or subtype (User or UserSubClass), even though it doesn't have to be. Otherwise, you end up with confusing and brittle code.

Clingstone

Thanks for your answer Chris. Indeed, I'm trying to check if it's a User or AnonymousUser. I've got the following method now: def _attempt(obj, action, actor, msg): actor.is_authenticated() if isinstance(actor, LazyObject): print type(actor) I'm passing a user, however the if condition is still true, actor is still a LazyObject. Why is this so ? – Selfdeceit

I realize I could do a try: on actor.isauthenticated() and then catch an AttributeException, which would indicate actor has no isauthenticated method (and thus is not an User). But I'm still a bit puzzled about why the snippet of code in my previous comment isn't working. – Selfdeceit

It is working, in one sense; __class__ is returning exactly what it should return, SimpleLazyObject, because that's what the class is. – Clingstone

If I understood your original response correctly, the SimpleLazyObject should be "woken up" into a User object when an attribute is accessed on it. So, I would have thought that calling .is_authenticated(), should have turned the object into a User. Hence my confusion at the if condition I list in the first comment being false. – Selfdeceit

(I've added the if statement I'm referring to to my original question, so it's easier to understand) – Selfdeceit

We've been speaking in simplistic terms, but in reality, request.user is always a SimpleLazyObject. The instantiated user (be it User or AnonymousUser) is stored as an attribute on it, and it merely proxies the request to most attributes on itself to attributes on the user object (__class__ being a notable exception). – Clingstone

Ahh I see. So using isInstance (which I assume just looks at __class__) on request.user will never work. Thank you for time. – Selfdeceit

I have created three subclasses of User. My user types are Admin, Employee and Relatives which are derivatives of User. For login, User model is used and multitable inheritance is being used. How do I convert request.user to one of the 3 types? – Laughton

request.user.is_authenticated is a property, not a function. – Nehemiah

Answer 2

This should do it:

# handle django 1.4 pickling bug
if hasattr(user, '_wrapped') and hasattr(user, '_setup'):
    if user._wrapped.__class__ == object:
        user._setup()
    user = user._wrapped

I had to write this so I could add a user to the session dictionary. (SimpleLazyObjects are not picklable!)

Ellieellinger

Answer 3

user= request.user._wrapped if hasattr(request.user,'_wrapped') else request.user

Then you use user instead of request.user.

This is similar to UsAaR33's answer, but a one-liner is nicer for converting the object.

Proterozoic

It is similar but it doesn't attempt to called _setup() on the user object if the _wrapped part isn't initialised properly. I think that UsAaR33's answer is preferable for this reason. – Dalpe

Answer 4

For anyone wanting to write a failing "small" unittest for your code, you can generate a wrapped User and stuff it inside a request.

from django.contrib.auth import get_user_model
from django.test import RequestFactory
from django.utils.functional import SimpleLazyObject

user = get_user_model().objects.create_user(
    username='jacob',
    email='jacob@…',
    password='top_secret',
)

factory = RequestFactory()
request = factory.get('/')
request.user = SimpleLazyObject(lambda: user)

See:

• https://github.com/django/django/blob/master/tests/utils_tests/test_lazyobject.py for current tests on the Lazy Objects.

• https://docs.djangoproject.com/en/dev/topics/testing/advanced/#django.test.RequestFactory for latest info on the RequestFactory.

Subsidiary

Answer 5

This might be helpful to others and a bit cleaner.

The python method isinstance(instance, class) returns if the SimpleLazyObject's contained instance is of the provided class.

if isinstance(request.user, User):
    user = request.user

Babbie

Answer 6

change your code like this and there should be no problem:

from copy import deepcopy

def _attempt(actor):
    actor = deepcopy(actor)
    if actor.__class__ != User:
        raise TypeError

Eno

Please add an explanation to what your changed code does and how it helps solve the original question. – Minority

Answer 7

This is the schema of the auth_user table in Django -

id
password
last_login
is_superuser
username
last_name
email
is_staff
is_active
date_joined
first_name

Now if you want id write like -

req.user.id

and if you want username write like -

req.user.username

Omer