How do I import the Django DoesNotExist exception?

How do I import the Django DoesNotExist exception?

I'm trying to create a UnitTest to verify that an object has been deleted.
from django.utils import unittest
def test_z_Kallie_can_delete_discussion_response(self):
  ...snip...
  self._driver.get("http://localhost:8000/questions/3/want-a-discussion") 
  self.assertRaises(Answer.DoesNotExist, Answer.objects.get(body__exact = '

User can reply to discussion.

')) I keep getting the error: DoesNotExist: Answer matching query does not exist.

Solutions/Answers:

Answer 1:

You don’t need to import it – as you’ve already correctly written, DoesNotExist is a property of the model itself, in this case Answer.

Your problem is that you are calling the get method – which raises the exception – before it is passed to assertRaises. You need to separate the arguments from the callable, as described in the unittest documentation:

self.assertRaises(Answer.DoesNotExist, Answer.objects.get, body__exact='<p>User can reply to discussion.</p>')

or better:

with self.assertRaises(Answer.DoesNotExist):
    Answer.objects.get(body__exact='<p>User can reply to discussion.</p>')

Answer 2:

You can also import ObjectDoesNotExist from django.core.exceptions, if you want a generic, model-independent way to catch the exception:

from django.core.exceptions import ObjectDoesNotExist

try:
    SomeModel.objects.get(pk=1)
except ObjectDoesNotExist:
    print 'Does Not Exist!'

Answer 3:

DoesNotExist is always a property of the model that does not exist. In this case it would be Answer.DoesNotExist.

Answer 4:

One thing to watch out for is that the second parameter to assertRaises needs to be a callable – not just a property. For instance, I had difficulties with this statement:

self.assertRaises(AP.DoesNotExist, self.fma.ap)

but this worked fine:

self.assertRaises(AP.DoesNotExist, lambda: self.fma.ap)

Answer 5:

self.assertFalse(Answer.objects.filter(body__exact='<p>User...discussion.</p>').exists())

Answer 6:

This is how I do such a test.

from foo.models import Answer

def test_z_Kallie_can_delete_discussion_response(self):

  ...snip...

  self._driver.get("http://localhost:8000/questions/3/want-a-discussion") 
  try:
      answer = Answer.objects.get(body__exact = '<p>User can reply to discussion.</p>'))      
      self.fail("Should not have reached here! Expected no Answer object. Found %s" % answer
  except Answer.DoesNotExist:
      pass # all is as expected

References