IntegrityError at /posts/new/

Question

I am new on this field and i am currently learning django and i come up with this problem. I am working on a project which is a social clone project and this project you can only post when you are in a group and i've encountered this problem when i post. The first post is working fine but the second post i get this error message called IntegrityError i've tried to delete my migrations and database and migrate and makemigrations again but does not fix the problem and now i am stuck and i hope someone will help me. This is the actual error

Posts Models

##########################
## POSTS MODELS.PY FILE ##
##########################

from django.contrib.auth import get_user_model
from django.db import models
from groups.models import Group
from misaka import html
from django.urls import reverse
from django.conf import settings

User = get_user_model()

class Post(models.Model):

    user = models.ForeignKey(User, related_name='posts', on_delete=models.CASCADE)
    created_at = models.DateTimeField(auto_now=True)
    message = models.TextField()
    message_html = models.TextField(editable=False)
    group = models.ForeignKey(Group, related_name='posts', null=True, blank=True, on_delete=models.CASCADE)

    def __str__(self):
        return self.message

    def save(self, *args, **kwargs):

        self.message_html = html(self.message)
        super().save(*args, **kwargs)

    def get_absolute_url(self):
        return reverse(
            'posts:single',
            kwargs={
                'username': self.user.username,
                'pk': self.pk
            }
        )

    class Meta:

        ordering = ['-created_at']
        unique_together = ['user', 'group']

Posts Views.py

#########################
## POSTS VIEWS.PY FILE ##
#########################

from django.contrib.auth import get_user_model
from braces.views import SelectRelatedMixin
from django.views import generic
from posts import models, forms
from django.http import Http404
from django.contrib.auth.mixins import LoginRequiredMixin
from django.urls import reverse_lazy
from django.contrib import messages

User = get_user_model()

class PostList(SelectRelatedMixin, generic.ListView):

    model = models.Post
    select_related = ('user', 'group')

class UserPost(generic.ListView):

    model = models.Post
    template_name = 'posts/user_post_list.html'

    def get_queryset(self):

        try:
            self.post_user = User.objects.prefetch_related('posts').get(
                username__iexact=self.kwargs.get('username')
            )

        except User.DoesNotExist:
            raise Http404

        else:
            return self.post_user.posts.all()

    def get_context_data(self, **kwargs):

        context = super().get_context_data(**kwargs)
        context['post_user'] = self.post_user
        return context

class PostDetail(SelectRelatedMixin, generic.DetailView):

    model = models.Post
    select_related = ('user', 'group')

    def get_queryset(self):

        queryset = super().get_queryset()
        return queryset.filter(
            user__username__iexact=self.kwargs.get('username')
        )

class CreatePost(LoginRequiredMixin, SelectRelatedMixin, generic.CreateView):

    model = models.Post
    fields = ('message', 'group')

    def form_valid(self, form):

        self.object = form.save(commit=False)
        self.object.user = self.request.user
        self.object.save()
        return super().form_valid(form)

class DeletePost(LoginRequiredMixin, SelectRelatedMixin, generic.DeleteView):

    model = models.Post
    select_related = ('user', 'group')
    success_url = reverse_lazy('posts:all')

    def get_queryset(self):

        queryset = super().get_queryset()
        return queryset.filter(user_id=self.request.user.id)

    def delete(self, *args, **kwargs):

        messages.success(self.request, ('Post Delete'))
        return super().delete(*args, **kwargs)

Groups Models.py

##########################
## GROUPS VIEWS.PY FILE ##
##########################

from django.contrib.auth import get_user_model
from django import template
from django.db import models
from django.utils.text import slugify
from misaka import html
from django.urls import reverse
from django.conf import settings

User = get_user_model()
register = template.Library()

class Group(models.Model):

    name = models.CharField(max_length=255, unique=True)
    slug = models.SlugField(allow_unicode=True, unique=True)
    description = models.TextField(blank=True, default='')
    description_html = models.TextField(editable=False, blank=True, default='')
    members = models.ManyToManyField(User, through='GroupMember')

    def __str__(self):
        return self.name

    def save(self, *args, **kwargs):

        self.slug = slugify(self.name)
        self.description_html = html(self.description)
        super().save(*args, **kwargs)

    def get_absolute_url(self):
        return reverse('groups:single', kwargs={'slug': self.slug})

    class Meta:
        ordering = ['name']

class GroupMember(models.Model):

    group = models.ForeignKey(Group, related_name='memberships', on_delete=models.CASCADE)
    user = models.ForeignKey(User, related_name='user_groups', on_delete=models.CASCADE)

    def __str__(self):
        return self.user.username

    class Meta:
        unique_together = ('group', 'user')

Groups Views.py

[![##########################
## GROUPS VIEWS.PY FILE ##
##########################

from django.contrib.auth.mixins import LoginRequiredMixin
from django.views import generic
from groups.models import Group, GroupMember
from django.urls import reverse
from django.shortcuts import get_object_or_404
from django.db import IntegrityError
from django.contrib import messages
from groups import models

class CreateGroup(LoginRequiredMixin, generic.CreateView):

    model = Group
    fields = ('name', 'description')

class SingleGroup(generic.DetailView):
    model = Group

class ListGroups(generic.ListView):
    model = Group

class JoinGroup(LoginRequiredMixin, generic.RedirectView):

    def get_redirect_url(self, *args, **kwargs):
        return reverse('groups:single', kwargs={'slug': self.kwargs.get('slug')})

    def get(self, request, *args, **kwargs):

        group = get_object_or_404(Group, slug=self.kwargs.get('slug'))

        try:
            GroupMember.objects.create(user=self.request.user, group=group)
        except IntegrityError:
            messages.warning(self.request, (f'Warning, Already A Member Of {group.name}.'))
        else:
            messages.success(self.request, (f'You Are Now A Member Of {group.name} Group.'))

        return super().get(request, *args, **kwargs)

class LeaveGroup(LoginRequiredMixin, generic.RedirectView):

    def get_redirect_url(self, *args, **kwargs):
        return reverse('groups:single', kwargs={'slug': self.kwargs.get('slug')})

    def get(self, request, *args, **kwargs):

        try:
            membership = models.GroupMember.objects.filter(
                user=self.request.user,
                group__slug=self.kwargs.get('slug')
            ).get()
        except models.GroupMember.DoesNotExist:
            messages.warning(self.request, ("You Can't Leave This Group Because You Aren't In It."))
        else:
            membership.delete()
            messages.success(self.request, ('You Have Successfully Left This Group.'))

        return super().get(request, *args, **kwargs)

Answer 1

Remove unique_together from your Post model. It means that only one Post object can have that particular user and model combination, that is why you are getting the integrity error.

Answer 2

The error which you are getting is all about the unique constraint.

unique_together = ['user', 'group']

Since you have defined in your model the unique_together attribute, you need to have unique rows of the combination for user and group. One user can post only once in a group and you are trying to post in the same group by the same user, that's why you are getting a unique constraint failed error.