Koen Bok wrote:
> I'd like to build object relations (Model classes) without saving them
> to the database to predict a price for a specific order. Let's say I
> have this:
>
> class Order(Model):
> id = models.AutoField(primary_key=True)
> number = models.IntegerField()
>
> def total(self):
> return sum([p.price for p in self.product_set])
>
> class Product(Model):
> id = models.AutoField(primary_key=True)
> order = models.ForeignKey(Order)
> price = models.DecimalField()
>
> order = Order(number=1)
>
> # Now the nex line throws an error if we did not save the order here
> order.product_set.create(Product(price=20.0))
>
> assert order.total() == 20.0
That would be very hard i think(relations work with primary keys and
typically primary keys are only exist after save.
An alternative solution is to make a method that takes a set of products
and produces total for them.
I'd proly put sum_products in an OrderManager or maybe ProductManger but
not bothering with that here.
class Order(Model):
id = models.AutoField(primary_key=True)
number = models.IntegerField()
def total(self):
return sum_products(self.product_set)
def sum_products(self, products):
# maybe some other logic here such as customer discount, tax
calc, etc.
return sum([p.price for p in products])
def test_sum_products(self):
order = Order(number=1)
product_list = [Product(price=20.0), ]
self.assertEqual( 20.0, order.sum_products(product_list) )
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