Set default value for field using class method in Django
I found many similar posts on the internet on this topic, but neither state is clearly an issue.
code
class Item(models.Model):
@classmethod
def get_next_item_number(cls):
return cls.objects.count() + 1
number = models.IntegerField(default=get_next_item_number)
Problem
When I access the Django admin panel, the textbox associated with the "number" field contains
<classmethod object at 0x7fab049d7c50>
So I tried to change the code above
class Item(models.Model):
@classmethod
def get_next_item_number(cls):
return cls.objects.count() + 1
number = models.IntegerField(default=get_next_item_number())
but when i start django server i get:
number = models.IntegerField(default=get_next_item_number())
TypeError: 'classmethod' object is not callable
I know all of this could have been prevented by declaring get_next_item_number () as an external function, but this solution is not neat for me because get_next_item_number () only applies to the Item class.
Is there a solution I am missing?
+3
source to share
2 answers
To overwrite __init__
your class method Item
and define a default value there, have a look at this code:
from django.db import models
class Item(models.Model):
number = models.IntegerField()
@classmethod
def get_next_item_number(cls):
return cls.objects.count() + 1
def __init__(self, *args, **kwargs):
super(Item, self).__init__(*args, **kwargs)
if not self.pk and not self.number:
self.number = Item.get_next_item_number()
And here's the output stream
>>> from your_app import models
>>> models.Item().save()
>>> models.Item().number
>>> 2
>>> models.Item().save()
>>> models.Item().number
>>> 3
>>> models.Item.objects.filter(id=1)[0].number #number only get its value from classmethod on new items
>>> 1
0
source to share