I’m developing a forum app with the structure “forum → subforum → topic → comment” and I need to allow authorized users to create topics and comments outside of the admin page. For topic creation, I use form.instance.author = self.request.user, which works fine. However, for comments, I also need to automatically set a Topic foreign key, and I’m running into issues retrieving it from self.kwargs.

I tried the following view in views.py:

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class AddComment(LoginRequiredMixin, DataMixin, CreateView):
    model = Comment
    form_class = AddCommentForm
    template_name = 'forum/addcomment.html'
    page_title = 'Leave a comment'
    success_url = reverse_lazy('topic')

    def form_valid(self, form):
        topic = self.model.objects.get(topic=self.kwargs['topic'])
        form.instance.author = self.request.user
        form.instance.topic = topic
        return super(AddComment, self).form_valid(form)

which results in a KeyError:

PLAINTEXTCopied
KeyError at /forum/production/topics/topic-scenario-timing-plan/add_comment/
'topic_id'
...

I also tried using lookups like topic = self.model.objects.get(topic__id=self.kwargs['topic_id']), but that didn’t work either. Interestingly, when I accessed a field not explicitly listed (e.g., topic_slug), the error message listed both “topic” and “topic_id” among available keys. I would like to inspect what’s in self.kwargs but haven’t found a way yet.

My questions are:

• What is the optimal way to auto-assign user and topic foreign keys in Django forms for topic and comment creation?
• (Optional) How do methods like get_form_kwargs, get_initial, and form_valid operate with forms, and which approach is best in different situations?

Below is additional context including my forms, models, and URLs configuration.

forms.py:

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from django import forms
from django.core.exceptions import ValidationError

from forum import models

class AddTopicForm(forms.ModelForm):
    subject = forms.CharField(label="Заголовок", max_length=100, min_length=7)
    first_comment = forms.CharField(label="Сообщение", widget=forms.Textarea())

    class Meta:
        model = models.Topic
        fields = ['subject', 'first_comment']

    def clean_subject(self):
        subject = self.cleaned_data['subject']
        if len(subject) > 100:
            raise ValidationError("Длина превышает 100 символов")
        if len(subject) < 7:
            raise ValidationError("Слишком короткое заглавие, требуется не менее 7 символов")
        return subject

class AddCommentForm(forms.ModelForm):
    content = forms.CharField(label="Text", max_length=2000, min_length=1, widget=forms.Textarea())

    class Meta:
        model = models.Comment
        fields = ['content']

models.py (Topic and Comment models):

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class Topic(models.Model):
    subject = models.CharField(verbose_name='Заголовок', max_length=255, unique=True)
    first_comment = models.TextField(verbose_name='Сообщение', max_length=2000, default='')
    slug = models.SlugField(default='', unique=True, max_length=25, editable=False)
    subforum = models.ForeignKey('Subforum',
                                 verbose_name='Раздел',
                                 on_delete=models.CASCADE,
                                 related_name='subforum')
    creator = models.ForeignKey(User,
                                verbose_name='Создатель темы',
                                on_delete=models.SET('deleted'),
                                related_name='creator')
    created = models.DateTimeField(auto_now_add=True)
    closed = models.BooleanField(default=False)
    objects = models.Manager()

    class Meta:
        ordering = ['id']
        verbose_name = 'Обсуждения'
        verbose_name_plural = 'Обсуждения'

    def __str__(self):
        return self.subject

    def save(self, *args, **kwargs):
        if not self.id:
            self.slug = f'topic-{slugify(self.subject)}'
            return super(Topic, self).save(*args, **kwargs)

    def get_absolute_url(self):
        return reverse('forum:topic', kwargs={'topic_slug': self.slug, 'subforum_slug': self.subforum.slug})

class Comment(models.Model):
    topic = models.ForeignKey('Topic',
                              verbose_name='Тема',
                              on_delete=models.CASCADE,
                              related_name='comments')
    author = models.ForeignKey(User,
                               verbose_name='Комментатор',
                               on_delete=models.SET('deleted'),
                               related_name='author')
    content = models.TextField(verbose_name='Текст', max_length=2000)
    created = models.DateTimeField(verbose_name='Дата публикации', auto_now_add=True)
    updated = models.DateTimeField(verbose_name='Дата изменения', auto_now=True)
    objects = models.Manager()

    class Meta:
        ordering = ['created']
        verbose_name = 'Комментарии'
        verbose_name_plural = 'Комментарии'

    def __str__(self):
        return f'Post of {self.topic.subject} is posted by {self.author.username}.'

urls.py:

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from django.urls import path

from forum.views import *

app_name = 'forum'

urlpatterns = [
    path('', SubForumListView.as_view(), name='forum'),
    path('<slug:subforum_slug>/', TopicListView.as_view(), name='subforum'),
    path('<slug:subforum_slug>/add_topic/', AddTopic.as_view(), name="add_topic"),
    path('<slug:subforum_slug>/topics/<slug:topic_slug>/', ShowTopic.as_view(), name='topic'),
    path('<slug:subforum_slug>/topics/<slug:topic_slug>/add_comment/', AddComment.as_view(), name="add_comment"),
    path('<slug:subforum_slug>/topics/<slug:topic_slug>/edit/<int:id>/', UpdateComment.as_view(), name="edit_comment"),
]`

Any insights or guidance on automatically assigning these foreign keys and understanding form method behaviors would be greatly appreciated.