django model field definition for hierarchy, GenericForm

I want to represent a model hierarchy of categories in django orm. So f.i. you could have categories such as:

TopCategory
    SubCategory1
        SubSubCategory
    SubCategory2

This is my field definition, which points to the parent category:

class Category(models.Model)
    parentcategory = models.OneToOneField('self', blank = True, null = True)

And I use a GenericForm in the view:

def detail(request, category_id):   
    categoryInstance = Category.objects.get(pk = category_id)   
    GenericForm = modelform_factory(Category)
    form = GenericForm(instance = categoryInstance)

    if request.method == 'POST':
        form = GenericForm(request.POST, instance = categoryInstance)
        if form.is_valid():
            form.save()

This does work, there is only one slight pr开发者_如何学Coblem. No category should be allowed to point to itself as a parent. The form renders a dropdown where all categories are listed however.

I did try something like this in the field definition:

limit_choices_to = Q('parentcategory_id' is not id)

But that gave me an error. I could probably check and present an error message to the user, but maybe someone knows another way?

django-mptt is recommended for working with hierarchies in django.