how to stop create view if already created django - django

Question

please help me in making this application in django project
Here is models.py file code
from django.db import models
from bio.models import Profile
class Question(models.Model):
name = models.TextField(max_length=500)
def __str__(self):
return self.name
class Answer(models.Model):
question = models.ForeignKey(Question, related_name='question', on_delete=models.CASCADE)
profile = models.ForeignKey(Profile, related_name='profile', on_delete=models.CASCADE)
text = models.TextField(max_length=400)
created_on = models.DateTimeField(auto_now_add=True,null=True)
def __str__(self):
return "{0} on {1}".format(self.question, self.profile)
class Meta:
db_table = 'answer'
constraints = [
models.UniqueConstraint(fields=['profile', 'text', 'question'], name='unique answer')
]
here is views.py file code
class DetailViewMixin(object):
details_model = None
context_detail_object_name = None
def get_context_data(self, **kwargs):
context = super(DetailViewMixin, self).get_context_data(**kwargs)
context[self.context_detail_object_name] = self.get_detail_object()
return context
def get_detail_object(self):
return self.details_model._default_manager.get(pk=self.kwargs['pk'])
class AnswerCreate(DetailViewMixin, CreateView):
details_model = Question
context_detail_object_name = 'question'
model = Answer
form_class = NewAnswerForm
template_name = "qna/answer.html"
success_url = reverse_lazy('qna:list')
def form_valid(self, form):
form.instance.profile_id = self.kwargs.get('pk')
form.instance.question_id = self.kwargs.get('pk')
return super().form_valid(form)
here is my forms.py code
from django import forms
from .models import Answer
class NewAnswerForm(forms.ModelForm):
class Meta:
model = Answer
fields = ['text',]
def clean(self):
try:
Answer.objects.get(text=self.cleaned_data['text'].lower())
raise forms.ValidationError('Answer exists!')
except Answer.DoesNotExist:
pass
return self.cleaned_data
where am I going wrong????
I want that if user answers one question then he couldn't answer it again
how can i do form validation if object is already created

Answer 1

Add a UniqueConstraint to Answer so no combination of Question and Profile can be repeated:
https://docs.djangoproject.com/en/3.1/ref/models/constraints/#django.db.models.UniqueConstraint