Django model field default from model method

Question

I want to give a model field default value from the a model method.

How can i do that ?

when i try this code

Class Person(models.Model):
    def create_id(self):
        return os.urandom(12).encode('hex')

    name = models.CharField(max_length = 255)
    id = models.CharField(max_length = 255,default = self.create_id)

I get NameError: name 'self' is not defined.

If i remove the 'self' i get that 'create_id' needs 1 parameter.

Does the id have to be unique? person_id = models.AutoField(primary_key=True ) Just as an idea. — Don, Jun 14 '13 at 20:57

score 9 · Answer 1 · answered Aug 12 '12 at 16:02

9

You can define global method like this:

def create_id():
    return os.urandom(12).encode('hex')

Class Person(models.Model):
   name = models.CharField(max_length = 255)
   id = models.CharField(max_length = 255,default = create_id)

answered Aug 12 '12 at 16:02

Rohan

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i would like to make method of the class. – yossi Aug 13 '12 at 07:18
Usually if you need it to be on the class, that means you probably need other model attributes. the `.save()` method would be the best for this. – Jacob Valenta Dec 20 '14 at 23:05

score 5 · Accepted Answer · answered Aug 13 '12 at 07:32

5

I ended up doing this: (removing the self from both)

Class Person(models.Model):
    def create_id():
        return os.urandom(12).encode('hex')

    name = models.CharField(max_length = 255)
    id = models.CharField(max_length = 255,default = create_id)

it is working, but i am not sure if this is the best or the right way.

answered Aug 13 '12 at 07:32

yossi

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This *looks* good. I also wonder if this is a good *practice.* – eugene Jul 23 '13 at 05:07
How is this working? I think you're missing `self` as the first parameter of `create_id`, and call it like this: `self.create_id()` instead of `create_id` – Paco Mar 31 '15 at 14:09
@eugene it's not good practice in the sense that id's might not be unique, and I'd guess it's supposed to be. – Fabio Oct 21 '15 at 23:49
odd that you can't use self to refer to a member funciton in a class. – MagicLAMP Dec 20 '15 at 04:17
It's a serialization issue for migrations – dave4jr Mar 30 '17 at 01:29

Django model field default from model method

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