Django中奇怪的“ DoesNotExist”异常

Question

There is a simple code:

    class City(models.Model):
        slug = models.SlugField(max_length=150, unique=True)
        name = models.CharField(max_length=255)


    class CityPart(models.Model):
        city = models.ForeignKey('City', related_name='rel_cityparts')
        slug = models.SlugField(max_length=150, unique=True)
        name = models.CharField(max_length=255)

        def __unicode__(self):
            #return self.name
            return u'%s (%s)' % (self.name, self.city.name)

I found that in __unicode__ method fails, leading to DoesNotExist exception. Django "thinks" the related city does not exist, thought it exists for sure. I have re-checked it, the DB is valid. I used Sqlite and Postgres, both loads\\dumps the DB data but both raises this exception. So I think it's related to some code issues, not to the DB inconsistency.

The full traceback is here (really uninformative): http://dpaste.com/hold/1429873/

When I'm checking the value in the file virtenv_macos/lib/python2.7/site-packages/debug_toolbar/panels/template.py , line 85 (*pformat(value)*) - it tells me that the "value" variable has the following value: *[broken repr (DoesNotExist)]*

MacOS, Python 2.7, Django 1.5.2

PS The exception raises when I'm trying to see the list of DB records (ListView), not when I'm trying to create a new one.

Answer 1

I think you shoud see this post.

If you are trying in create a CityPart instance and call the ____unicode____ method and you haven't set the city, it'll raise an exception.

your bad code could be:

c = CityPart()
c  # This fail because you don't set the City!


#  try that
city = City(name='foo', slug='fooslug')
city.save() 
c = CityPart(city=city, name='bar')
c  # MAYBE this works, maybe

try to do not use the city in the ____unicode____ method:

class City(models.Model):
    slug = models.SlugField(max_length=150, unique=True)
    name = models.CharField(max_length=255)


class CityPart(models.Model):
    city = models.ForeignKey('City', related_name='rel_cityparts')
    slug = models.SlugField(max_length=150, unique=True)
    name = models.CharField(max_length=255)

    def __unicode__(self):
        #return self.name
        return u'%s' % (self.name,)

Sorry my english. Hope helps!

Answer 2

It was because of the django-debug-toolbar app, it's "debug_toolbar.middleware.DebugToolbarMiddleware" middleware. Don't have time to debug it, unfortunately. Just commented it out.