My Discount model describes common fields for all types of discounts in the system. I have some proxy models which describe concrete algorithm for culculating total. Base Discount class has a member field named type, which is a string identifing its type and its related class.
class Discount(models.Model):
TYPE_CHOICES = (
('V', 'Value'),
('P', 'Percentage'),
)
name = models.CharField(max_length=32)
code = models.CharField(max_length=32)
quantity = models.PositiveIntegerField()
value = models.DecimalField(max_digits=4, decimal_places=2)
type = models.CharField(max_length=1, choices=TYPE_CHOICES)
def __unicode__(self):
return self.name
def __init__(self, *args, **kwargs):
if self.type:
self.__class__ = getattr(sys.modules[__name__], self.type + 'Discount')
super(Discount, self).__init__(*args, **kwargs)
class ValueDiscount(Discount):
class Meta:
proxy = True
def total(self, total):
return total - self.value
But I keep getting exception of AttributeError saying self doesnt have type. How to fix this or is there another way to achieve this?
Your init method needs to look like this instead:
def __init__(self, *args, **kwargs):
super(Discount, self).__init__(*args, **kwargs)
if self.type:
self.__class__ = getattr(sys.modules[__name__], self.type + 'Discount')
You need to call super's __init__ before you will be able to access self.type.
Becareful with calling your field type since type is also a python built-in function, though you might not run into any problems.