我正在開發一個小型 django 項目，為此我創建了一項功能，允許用戶創建然后加入該組。現在，問題來了：每當我離開小組并嘗試重新加入它時，它都會顯示我在問題中提到的錯誤“唯一約束失?。篻roups_groupmember.group_id，groups_groupmember.user_id”這是我的加入課程：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'))        from sqlite3 import IntegrityError        try:            # GroupMember.objects.create(group=group)            GroupMember.objects.create(user=self.request.user, group=group)        except IntegrityError:            messages.warning(self.request, 'already a member!')        else:            messages.success(self.request, 'You are now a member!')        return super().get(request, *args, **kwargs)這是我的models.pyfrom django.db import modelsfrom django.utils.text import slugifyfrom django.urls import reverse# Create your models here.# GROUPS MODELS.PYimport markdownfrom django.contrib.auth import get_user_model  # returns user model that currently active in this projectUser = get_user_model()from django import templateregister = template.Library()class Group(models.Model):    name = models.CharField(max_length=256, unique=True)    slug = models.SlugField(allow_unicode=True, unique=True)    description = models.TextField(blank=True, default='')    description_html = models.TextField(editable=False, default='', blank=True)    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 = markdown.markdown(self.description)        super().save(*args, **kwargs)    def get_absolute_url(self):        return reverse('groups:single', kwargs={'slug': self.slug})    class Meta:        ordering = ['name']你能幫我解決這個問題嗎？謝謝 ！:)