Question

I have the following models in my Django app:

class Property(models.Model):
    ...various attributes...

class Booking(models.Model):
    property = models.ForeignKey(
        Property
    )
    ...more attributes...

I implemented the clean() method for Booking which checks various constraints of a Booking. A number of these constraints depend on the association of Booking and Property being in place. For that reason I have the following in the clean() method of Booking:

if self.property is not None:
    ...Property related validations...

Upon entering a new booking in the admin application and just pressing the Save button without entering anything, this generates a DoesNotExist exception on self.property is not None. It’s my understanding that the missing association should be captured by the individual field validation of Django.

When I comment out the clean() method the above doesn’t happen and the missing association is properly flagged as an error when I submit a blank booking form.

I’m obviously missing something but haven’t got a clue what…

Answer 1

Posting as an answer since it was the answer:

Have you tried changing your conditional to:

if hasattr(self, 'property') and self.property is not None

I’m not sure of the root cause since I deduced the solution based on the error message. I imagine that the Django ORM might create the foreign key association dynamically upon save, so even though it’s a required attribute it hasn’t been created yet since the Booking instance is new and hasn’t been saved.