Hi,
I think you are doing it right. I would remove the PurchaseOrderTotal model
however. The reason for this is that the purchase order itself should know
it's total and so on. Either you can add a signal on the save of the
PurchaseOrderItem - and update the PurchaseOrder total or the PurchaseOrder
could calculate the total when required via a method.
I think the easiest way would be to add a method that calculates the total:
@property
def subtotal(self):
order_total = 0
for item in self.purchaseorderitem_set.all():
order_total += item.qty * item.unit_price
return order_total
Now it is a property on the purchase order. So calling:
purchase_order.subtotal will get the total for the purchase order.
2 other things:
1. You can remove the amount in the PurchaseOrderItem and calculate the
total for the row when required (see my example above) - this of course
depends on WHEN you want to show the total. The same thing goes for
calculating the total on the PurchaseOrder. You could add a property the
same way I did for the PurchaseOrder in the PurchaseOrderItem class.
2. The names you have given your properties that are foreign keys are not
that good from an object oriented perspective. I would for example call the
invoice_number field on the PurchaseOrder as "invoice". The same goes for
the po_number_fk fields. Because when you assign them or when you want to
get a value from the invoice it would be easier to read -
purchase_order.invoice.id than purchase_order.invoice_number.id.
Hope that helps somewhat.
If you don't want to calculate the total each time (it all depends on the
usage), you can use signals to see when a model is saved/created and then
update the subtotal in the PurchaseOrder. See here for information about
signals: https://docs.djangoproject.com/en/2.0/topics/signals/
Andréas
2018-08-02 19:27 GMT+02:00 Alexander Joseph <alexander.v.jos...@gmail.com>:
> I've been working on a Purchase Order app but I'm getting a little
> confused how I'm going to put it all together.
>
> I have 3 models -
>
> class PurchaseOrder(models.Model):
> po_number = models.IntegerField(default=get_po_number, unique=True)
> po_date = models.DateField()
> invoice_number = models.ForeignKey(Invoice, on_delete=models.CASCADE)
> ....
>
>
> class PurchaseOrderItem(models.Model):
> po_number_fk = models.ForeignKey(PurchaseOrder,
> on_delete=models.CASCADE)
> qty = models.IntegerField()
> unit = models.CharField(max_length=100, blank=True, null=True)
> description = models.CharField(max_length=255)
> unit_price = models.DecimalField(max_digits=6, decimal_places=2)
> amount = models.DecimalField(max_digits=6, decimal_places=2)
>
>
> class PurchaseOrderTotal(models.Model):
> po_number_fk = models.ForeignKey(PurchaseOrder,
> on_delete=models.CASCADE)
> subtotal = models.DecimalField(max_digits=6, decimal_places=2)
> tax = models.DecimalField(max_digits=6, decimal_places=2,
> default="7.82")
> shipping = models.DecimalField(max_digits=6, decimal_places=2)
> other = models.DecimalField(max_digits=6, decimal_places=2)
> total = models.DecimalField(max_digits=6, decimal_places=2)
>
>
> the first (PurchaseOrder) holds information about the purchase order
> itself. ie. what the invoice number is, the vendor, etc.
> the second (PurchaseOrderItem) lists items in the purchase order to
> purchase
> the third (PurchaseOrderTotal) totals up the amounts from the items and
> adds tax etc. (I may not need this model.. I can probably put this info in
> the first model?)
>
>
> Does it look like I'm going about this in the right way or should I take
> away the third model and put those fields from the third model into the
> first model? How do I total up all prices for all items? I'm sure I'll need
> to do some sort of loop to total up all prices but where do I do that? In
> the form_valid fucntion? or do I override the save function and do it
> there? Thanks!
>
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