Catching DoesNotExist exception in a custom manager in Django

Question

I have a custom manager for a Django model. I don't seem to be able to catch DoesNotExist exception here. I know how to do it inside the model but it didn't work here:

class TaskManager(models.Manager):
    def task_depend_tree(self, *args, **kwargs):
        if "id" in kwargs:
            try:
                task = self.get(id=kwargs["id"])
            except DoesNotExist:
                raise Http404

Get_object_or_404 doesn't work either. What is wrong here?

What does "doesn't work" mean, for both those cases? What actually happens? — Daniel Roseman, Jan 10 '13 at 10:26
@DanielRoseman NameError: global name 'DoesNotExist' is not defined — Seperman, Jan 10 '13 at 18:33

score 146 · Accepted Answer · answered Jan 10 '13 at 15:18

146

Try either using ObjectDoesNotExist instead of DoesNotExist or possibly self.DoesNotExist. If all else fails, just try and catch a vanilla Exception and evaluate it to see it's type().

from django.core.exceptions import ObjectDoesNotExist

answered Jan 10 '13 at 15:18

Jeff Triplett

2,216
1
16
8

I had tried Self.DoesNotExist and it failed. The error I get when something doesn't exist in database is: `NameError: global name 'DoesNotExist' is not defined` So I need to import DoesNotExist from somewhere. I assumed it is in models.Model but models.Model.DoesNotExist didn't work. – Seperman Jan 10 '13 at 18:43
self.DoesNotExist will obviously not help, because self exists if it has such a method. Use instead `task.DoesNotExist` or `ObjectDoesNotExist`. – Philipp Zedler Jan 11 '13 at 09:02
Did you try my suggestion of `ObjectDoesNotExist`? The other syntax might be self.model.DoesNotExist... but I'm not sure off the top of my head. – Jeff Triplett Jan 11 '13 at 17:10
13

I had to import ObjectDoesNotExist and it worked to catch DoesNotExist: `from django.db.models.base import ObjectDoesNotExist ` Thanks! – Seperman Jan 17 '13 at 07:23

score 18 · Answer 2 · answered May 04 '14 at 19:46

As panchicore suggested, self.model is the way to go.

class TaskManager(models.Manager):
    def task_depend_tree(self, *args, **kwargs):
        if "id" in kwargs:
            try:
                task = self.get(id=kwargs["id"])
            except self.model.DoesNotExist:
                raise Http404

score 6 · Answer 3 · answered Mar 10 '17 at 13:38

If you need to implement this on a list method (DRF) using GenericViewSet, and need an empty list to be returned, use this:

    def list(self, request, *args, **kwargs):
    self.get_object() # I use this to trigger the object_permission
    try:
        queryset = self.queryset.filter(user=(YourModel.objects.get(user=request.user).user))
    except YourModel.DoesNotExist:
        return Response(YourModel.objects.none())

    serializer = YSourModelSerializer(queryset, many=True)
    return Response(serializer.data)

This is the cleanest way of handling this exception since it does not involve importing the Exception — Robert Killkelley, Jan 25 '21 at 23:15

panchicore · Answer 4 · 2019-01-31T19:13:10.593

2

you can use the DoesNotExist from the Manager.model (self.model) instance, when you say objects = MyManager() you are assigning self.model inside MyManager class.

        try:
            task = self.get(id=kwargs["id"])
            return task
        except self.DoesNotExist:
            return None

edited Jan 31 '19 at 19:13

answered Sep 07 '13 at 14:16

panchicore

11,451
12
74
100

This will not work. You have to use self.model.DoesNotExist – Sudhakaran Packianathan Jun 03 '17 at 06:25

score 1 · Answer 5 · answered May 27 '21 at 03:13

In Django, every object from model has an exception property DoesNotExists. So you can call it from the object itself or from the exceptions module.

From object (self):

from django.db import models

class TaskManager(models.Manager):
    def task_depend_tree(self, *args, **kwargs):
        if "id" in kwargs:
            try:
                task = self.get(id=kwargs["id"])
            except self.model.DoesNotExist:
                raise Http404

From exceptions module:

from django.core.exceptions import ObjectDoesNotExist

try:
    return "Calling object"
except ObjectDoesNotExist:
    raise Http404

score 0 · Answer 6 · answered May 30 '20 at 23:22

0

I handle the exception this way and it worked.

from django.core.exceptions import ObjectDoesNotExist

try:
    task = self.get(id=kwargs["id"])
except ObjectDoesNotExist as DoesNotExist:
    raise Http404

answered May 30 '20 at 23:22

Santi Rodriguez

164
1
9

The name DoesNotExist is quite misleading here and not used at all – rapto Nov 08 '21 at 12:31

Catching DoesNotExist exception in a custom manager in Django

6 Answers6