you can use count() in views or models to count number of objects then add the new record
On Tue, 24 Jul 2018, 02:55 Alexander Joseph, <[email protected]> wrote: > Thanks Michael and Gerald. With an auto key field or primary key field > would users still be able to input their own value? And if so how would I > be able to give it a default attribute in a form that shows what the next > number should be, if the user decides to choose to use the auto increment? > Thanks again > > On Mon, Jul 23, 2018, 6:36 PM Gerald Brown <[email protected]> wrote: > >> From >> "https://docs.djangoproject.com/en/2.0/topics/db/models/#automatic-primary-key-fields"; >> <https://docs.djangoproject.com/en/2.0/topics/db/models/#automatic-primary-key-fields>, >> it has a further definition of automatic primary key fields. In your model >> just add "(primary_key=True)" to po_number field. >> >> On Tuesday, 24 July, 2018 07:54 AM, Michael MacIntosh wrote: >> >> Hi, >> >> Aren't you looking for the AutoField? >> >> https://docs.djangoproject.com/en/2.0/ref/models/fields/#autofield >> >> It will automatically increment based on each record added to the table. >> >> >> As an aside, the problem you are having is that in python, the first >> argument to a class is a reference to the instance of that class. In C >> this is often called a context. In C++ and Java it would be like the >> `this` pointer. So you wouldn't generally pass "self" to a class member. >> >> Hope that helps! >> >> On 7/23/2018 1:39 PM, Alexander Joseph wrote: >> >> Hello, >> >> I have a model ... >> >> class PurchaseOrder(models.Model): >> po_number = models.IntegerField(unique=True) >> >> >> and a function ... >> >> def get_po_number(self, *args, **kwargs): >> if not self.id: >> last_po = PurchaseOrder.objects.order_by('po_number').last() >> if last_po: >> last_po_num = last_po.po_number[-2:] >> new_po_num = int(last_po_num) + 1 >> else: >> new_po_num = '0001' >> self.po_number = new_po_num >> return self.po_number >> >> >> what I'm trying to do is use the get_po_number() function to get a >> default value for the po_number field in the model. However when I set the >> default in the model like so... >> >> class PurchaseOrder(models.Model): >> po_number = models.IntegerField(unique=True, >> default=get_po_number(self)) >> >> it says "NameError: name 'self' is not defined" >> >> >> What am I doing wrong? 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