Django - Assign & limit every logged-in user to create only one instance

Question

How to limit every logged-in user to create only one instance/object from the frontend?

here's my model looks like:

class MyModel(models.Model):
    u_name = models.OneToOneField(User, on_delete=models.CASCADE)
    category = models.ForeignKey(Category, blank=True, null=True, on_delete=models.CASCADE)
    ...
    ...
    my_linkedin = models.URLField(unique=True, blank=True, null=True)
    my_price = models.CharField(max_length=20, default=0)

    joined = models.DateTimeField(default=now, editable=False)

    def __str__(self):
        return self.my_name

    def clean(self):
        model = self.__class__
        if model.objects.count() > 0 and \
                self.id != model.objects.get().u_name_id:
            print('hell')
            raise ValidationError("You can only create 1 profile ")

my views:

class MyCreateView(LoginRequiredMixin, CreateView):
    model = MyModel
    fields = [
        'category',
        ....
        ....
    ]
    template_name = 'index/form.html'
    success_url = '/'

    def form_valid(self, form):
        form.instance.u_name = self.request.user
        return super().form_valid(form)

And my form:

class MyModelForm(forms.ModelForm):
    class Meta:
        model = MyProfile
        fields = '__all__'
        exclude = ['u_name']

The problem is, that the current code here, they can't assign on every logged-in user. So when I try to login using a different user, The error looks like:

get() returned more than one MyModel -- it returned 3!

How can I achieve this?

Answer 1

   def clean(self):
      model = self.__class__
        if model.objects.count() > 0 and \
                self.id != model.objects.get().u_name_id:
            print('hell')
            raise ValidationError("You can only create 1 profile ")

model.objects.get() -> This is the cause of this error. get() must return only one object from this table. But this table has 3 rows from what I can see. You must add parameters in get function returning one object then you can access this object u_name_id. Like this:

   if model.objects.count() > 0 and model.objects.filter(u_name_id = self.u_name_id).count > 0:
   print("hell")
   raise ValidationError("You can only create 1 profile ")

Or:

from django.core.exceptions import ObjectDoesNotExist
.
.
.
   if model.objects.count() > 0:
       try:
          obj = model.objects.get(u_name_id = self.u_name_id)
          print("hell")
          raise ValidationError("You can only create 1 profile ")
       except ObjectDoesNotExist:
          pass # this is not problem for you because this user have not object