How to construct url path with two detailview - django

Question

I have following url patterns
urlpatterns = [
path('', CategoryListView.as_view(), name='forum'),
path('category/<int:pk>/', CategoryDetailView.as_view(), name='forum-detail'),
]
Inside the CategoryDetailView I will list the posts related to that category. So, when I click the any of the post I want the post detail view inside the category, because when I will create post with CreateView class I want category already predefined. I could also do the following
path('post/<int:pk>/', ForumPostDetailView.as_view(), name='forum-post-detail'),
path('post/new/', ForumPostCreateView.as_view(), name='forum-post-create'),
]
In this case user should choose the category by himself when he or she will try to create the post. But I want the category to be chosen already something like this ( I know this is wrong)
path('category/<int:pk>/post/<int:pk>/', ForumPostDetailView.as_view(), name='forum-post-detail'),
path('category/<int:pk>/post/new/', ForumPostCreateView.as_view(), name='forum-post-create'),
]
my view file and models are like this:
class ForumPostCreateView(CreateView):
model = PostForum
fields = ['title', 'content']
template_name = 'forum/forum_post_form.html'
def form_valid(self, form):
form.instance.author = self.request.user
return super().form_valid(form)
class Category(models.Model):
image = models.ImageField(default='category.png', upload_to='category_pics')
title = models.CharField(max_length=100)
content = models.CharField(max_length=1200)
date_posted = models.DateTimeField(auto_now=True)
class PostForum(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE)
title = models.CharField(max_length=100)
content = models.TextField()
date_posted = models.DateTimeField(default=timezone.now)
author = models.ForeignKey(User, on_delete=models.CASCADE)
So how to do it? Now it shows
IntegrityError
null value in column "category_id" violates not-null constraint

Answer 1

Set the category.id in urls.py
path('category/<int:cat_id>/post/new/', ForumPostCreateView.as_view(), name='forum-post-create')
check if it exists in your view
class ForumPostCreateView(CreateView):
category = None
def despatch(self, *args, **kwargs):
super().despatch(*args, **kwargs)
if 'cat_id' in self.kwargs:
self.category = Category.objects.get(id=cat_id)
Now you can use it in your form when you initialise the form