django many to many validation when add()

Question

Hi

i have a Category model with parent/child self relation For primary category and sub categories :

class Place(models.Model):
    name = models.CharField(_("name"), max_length=100)
    categories = models.ManyToManyField("Category", verbose_name=_("categories"))

class Category(models.Model):
    name = models.CharField(_("name"), max_length=100)
    parent = models.ForeignKey('self', blank=True, null=True, related_name='child_set')

i need to prevent orphans, to prevent this kind of errors (in admin web interface)

c_parent = Category(name='Restaurant')
c_parent.save()

c_child = Category(name="Japanese restaurant", parent=c_parent)
c_child.save()

place1 = Place (name="Planet sushi")
place1.save()
place1.categories.add(c_parent)
place1.categories.add(c_child)

So now we have a new Place called "Planet sushi", it's a Restaurant (root category), and a Japanese Restaurant (sub category)

but i want to prevent this kind of things :

place2 = Place (name="Tokyofood")
place2.save()

place2.categories.add(c_child)

because parent is not set, or is not the correct parent category

where can i do form validation for the admin ? and other forms (because any user can add a new place and will have to choose correct categories for)

Answer 1

update:

in Place class add this method:

def add_cat(self,cat):
    self.categories.add(cat)
    if cat.parent:
        self.add_cat(cat.parent)

now instead of using place1.categories.add(cat) you can use place1.add_cat(cat) and it will automatically add the category, and its parent category, and its parent category and so on. this is not tested, but even if it doesn't work it should get the point across.