Django generate custom cheque number

Question

I'm new in django, I want to create custom Cart number that starts with #. When a new record comes into database. #1-1000, #1-1001, #1-9999, .... #2-1000, ...#2-9999 etc.

This is my model
class Cart(models.Model):
    # id = models.CharField(primary_key=True, editable=False, max_length=10)
    user = models.ForeignKey(Customer, on_delete=models.CASCADE, related_name="cart")
    create_date = models.DateField(auto_now_add=True)
    cart_number = models.CharField(max_length=500, default=increment_cart_number, null=True, blank=True)
    total_summa = models.FloatField()
    time = models.TimeField(auto_now_add=True)

The cart_number will be always in range 1000- 9999 so how can I do that with increment_cart_number function?

This may help you [https://stackoverflow.com/a/52070665/16475089](link) — ilyasbbu, Oct 07 '22 at 05:48

NixonSparrow · Answer 1 · 2022-10-07T08:34:01.550

0

Create a function, that finds a next cart_number:

class Cart(models.Model):
    ...
    def get_next_cart_number(self):
        cart_query = Cart.objects.filter(cart_number__isnull=False)
        if not cart_query:
            return '#1-1000'
        number = list(map(int, cart_query.last().cart_number.replace("#", "").split("-")))
        if number[1] == 9999:
            number[0] += 1
            number[1] = 1000
        return f"#{number[0]}-{number[1]}"

Then add signals, so it will be set just at the creation. Create file signals.py inside the app:

from my_app.models import Cart
from django.db.models.signals import post_save
from django.dispatch import receiver

@receiver(post_save, sender=Cart)
def create_user_profile(sender, instance, created, **kwargs):
    if created and not instance.cart_number:
        instance.cart_number = instance.get_next_cart_number()
        instance.save()

And import signals file inside your apps.py in the same app:

class MyAppConfig(AppConfig):
    ...
    def ready(self):
        from . import signals

In this way every time you will create Cart object, just after his first save (created variable tells it that) it will find and set a new cart number. Remember, that it's important that you keep blank=True and null=True attributes.

edited Oct 07 '22 at 08:34

answered Oct 07 '22 at 06:07

NixonSparrow

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this error `'NoneType' object has no attribute 'replace'` – Xursandbek Ibadullayev Oct 07 '22 at 06:24
Ok, it happened, because you had no number there. Change `Cart.objects.last()` to `Cart.objects.filter(cart_number__isnull=False).last()`. – NixonSparrow Oct 07 '22 at 06:41
Thank you , it works but i can't rate you "You need at least 15 reputation to cast a vote, but your feedback has been recorded." return message – Xursandbek Ibadullayev Oct 07 '22 at 07:48
@XursandbekIbadullayev as an author of the question you can tick answer as positive. Good luck with further work! – NixonSparrow Oct 07 '22 at 08:14
And you actually don't need signals, you can name method `increment_cart_number` instead `get_next_cart_number` as you preffered in the beginning and it should work. – NixonSparrow Oct 07 '22 at 08:35

score 0 · Accepted Answer · edited Oct 07 '22 at 07:59

0

def increment_cart_number():
    last_cart_number = Cart.objects.last()
    if last_cart_number.exists():
       last_num = last_cart_number.cart_number.replace('#','').split('-')
       if int(last_num[1]) >= 9999:
          first_number = int(last_num[0]) + 1
          secound_number = 1000
          result = '#' +str(first_number)+ '-' +str(secound_number)
          return result
       elif int(last_num[1]) < 9999:
           secound_number = int(last_num[1]) + 1
           result = '#'+ last_num[0]+ '-' +str(secound_number)
           return result
     else:
         return '#1-1000'

But I suggest to you for more cleaner way and best practice to do it in another way:

Make this field as AutoField and make defalut value 1000 to start from it.

cart_number = models.AutoField(auto_created = True, default=1000)

After that when you want to print this value add '#' to it from frontend that will be better and faster and easier.

edited Oct 07 '22 at 07:59

Sunderam Dubey

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answered Oct 07 '22 at 06:24

Hashem

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but should start with #2-1000 when default is 9999 – Xursandbek Ibadullayev Oct 07 '22 at 06:39
I edited it, you can use it now as you want – Hashem Oct 07 '22 at 07:20
'NoneType' object has no attribute 'cart_number' , now it gives the error – Xursandbek Ibadullayev Oct 07 '22 at 07:27
edited again the error 'NoneType' because you don't have any data before – Hashem Oct 07 '22 at 07:35

Django generate custom cheque number

2 Answers2