Trying to build a purchase order app - django

Question

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!

Answer 1

I would combine model 1 and 3. You can total up the numbers when you submit the form and then save it to the same model. Its better to try and keep all related model information on the same table. If you find out after testing that for some reason one model doesn't work well you can always change it.
There are multiple ways to total up the totals:
Do it in your view when you submit the form and save it to the DB.
This would be my recommended choice for your situation since this data while not likely
change very often.
Do not save the totals in the DB and
sum them up in your view before you display that information.
Do not save the totals in the DB and sum them up in your
template.
I would highly discourage the third option since your sounds like your data is fairly static and there is no need to do that processing in your template. I added it to illustrate all the possibilities. This also applies to the second option, though in this situation option two is better than three because it is done in the view instead the template but is still not the best option since it would not make since to do that calculation over and over again for data that never changed.
Example:
def your_view(request):
if request.method == 'POST':
# create a form instance and populate it with data from the request:
form = InvoiceForm(request.POST)
# check whether it's valid:
if form.is_valid():
tax = form.cleaned_data.get('tax')
sub = form.cleaned_data.get('sub_total')
fee = form.cleaned_data.get('fee')
form.total = tax + sub + fee
form.save()
return HttpResponseRedirect('/thanks/')
# if a GET (or any other method) we'll create a blank form
else:
form = InvoiceForm()
return render(request, 'name.html', {'form': form})