Prometheus Prometheus - 2 months ago 57
Python Question

Django check if a related object exists error: RelatedObjectDoesNotExist

I have a method

in my model that needs to check if a related object exists

class Business(base):
name = models.CharField(max_length=100, blank=True, null=True)

def has_related_object(self):
return (self.customers is not None) and ( is not None)

class Customer(base):
name = models.CharField(max_length=100, blank=True, null=True)
person = models.OneToOneField('Business', related_name="customer")

But I get the error:


RelatedObjectDoesNotExist: Business has no customer.


This is because the ORM has to go to the database to check to see if customer exists. Since it doesn't exist, it raises an exception.

You'll have to change your method to the following:

def has_related_object(self):
    has_customer = False
        has_customer = (self.customers is not None)
    except Customer.DoesNotExist:
    return has_customer and ( is not None)

I don't know the situation with so I'll leave it to you to adjust it if it needs it.

Side note: If you were doing this on a model that has the ForeignKeyField or OneToOneField on it, you would be able to do the following as a shortcut to avoid the database query.

def has_business(self):
    return self.business_id is not None