I'm working on very badly designed legacy database. On some of the tables not only can the foreign keys be null (which is OK) they can be 0 too.
I mapped one of these tables to a Model it returns the desired None value when it is Null in the table but raises an exception when the value is 0.
Is there a way to make it return None on foreign keys containing the value 0.
Faced the same problem, so end up with writing ForeignKey subclass:
class LegacyForeignKey(models.ForeignKey):
"""
ForeignKey for legacy databases where foreign keys columns
are non-nullable and using zero values as NULL.
class Order(models.Model):
carrier = LegacyForeignKey('Carrier', null=True)
class Meta:
managed = False
db_table = "ps_order"
order.carrier_id = 0
order.carrier # no Carrier.DoesNotExist exception
"""
def get_local_related_value(self, instance):
ret = super().get_local_related_value(instance)
return [None if item == 0 else item for item in ret]
You'd have to create your own ForeignKey-like field that would not choke on a 0. Note that any non-NULL value could be valid, so your data is in the wrong here, and you should consider repairing it.
