How to automatically fill out an auto increment number in form field?

[Alexander Joseph]

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? Thanks!

[Michael MacIntosh]

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!

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[Gerald Brown]

From "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.

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[Alexander Joseph]

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

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[mottaz hejaze]

you can use count() in views or models to count number of objects then add the new record

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[Alexander Joseph]

For future reference - I had to change my function to

def get_po_number():

    last_po = PurchaseOrder.objects.order_by('po_number').last()

    if last_po:

        last_po_num = last_po.po_number

        new_po_num = last_po_num + 1

    else:

        new_po_num = '1'

    po_number = new_po_num

    return po_number

class PurchaseOrder(models.Model):

    po_number = models.IntegerField(unique=True, default=get_po_number)

And the default value should be set to get_po_number

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