Matching query does not exist when retrieving object by slug

[Viet Phuong]

(My English is not so good so I'll just try to be simple, sorry guys)

So I have a model TopList which has a slug field so I can look up its object by slug.

class TopList(models.Model):
    name = models.CharField(max_length=200)
    slug = models.SlugField(max_length=200, default='')

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.set_slug()

    def save(self, *args, **kwargs):
        super().save(*args, **kwargs)
        self.set_slug()

    def set_slug(self):
        self.slug = slugify(self.name, allow_unicode=True)

The problem is when I use a ModelForm to create object, the slug field is set correctly, but when I use it to look up the object, it returns "lists.models.DoesNotExist: TopList matching query does not exist" (I tried it in the shell):

# forms.py
class TopListForm(ModelForm):
    class Meta:
        model = TopList
        fields = ('name',)

# Item is just a model which has foreignkey relationship with TopList
ItemFormSet = inlineformset_factory(TopList, Item, fields=('name',))

# views.py
def new_list(request):
    form = TopListForm()
    item_formset = ItemFormSet()

    if request.method == 'POST':
        form = TopListForm(request.POST)
        if form.is_valid():
            created_list = form.save(commit=False)
            item_formset = ItemFormSet(request.POST, instance=created_list)
            if item_formset.is_valid():
                created_list.save()
                item_formset.save()
                return redirect('/danh-sach')

    return render(request, 'lists/new_list.html', context={'form': form, 'item_formset': item_formset})

But if I use TopList.objects.create(name='something') to create object, slug is still set correctly, and I can retrieve it by slug.

# "test test" is an object I created earlier using form
>>> TopList.object.get(slug='test-test')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
AttributeError: type object 'TopList' has no attribute 'object'
>>> TopList.objects.get(slug='test-test')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/vietphuong/Documents/Python/toptenproject/venv/lib/python3.5/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/vietphuong/Documents/Python/toptenproject/venv/lib/python3.5/site-packages/django/db/models/query.py", line 385, in get
    self.model._meta.object_name
lists.models.DoesNotExist: TopList matching query does not exist.
>>> TopList.objects.create(name='another test')
<TopList: another test>
>>> TopList.objects.get(slug='another-test')
<TopList: another test>

Another thing is after I try to save that "test test" object, just save no changing at all, I can now look it up.

>>> TopList.objects.get(name='test test')
<TopList: test test>
>>> t = TopList.objects.get(name='test test')
>>> t.slug
'test-test'
>>> t.save()
>>> TopList.objects.get(slug='test-test')
<TopList: test test>

[Antonis Christofides]

Hello,

you have an error here:

    def save(self, *args, **kwargs):
        super().save(*args, **kwargs)
        self.set_slug()


self.set_slug() should be before super().save().

Regards,

Antonis Christofides
http://djangodeployment.com

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