如何使用默认属性向现有Django Model添加非null唯一值

Question

I need to add slug field to django model, and i thing it's better when it not null. So i'm trying to add slug to model

slug = models.SlugField(
    'URL',
    unique=True,
    default=id_generator,
)

my id_generator:

import string
import random
def id_generator():
    size=16
    chars=string.ascii_lowercase + string.digits
    return ''.join(random.choice(chars) for x in range(size))

The problem is when i migrate changes. Method id_generator is calling one time and uses the same value for all model objects. So i have dupliicate entrie in unique field. How can i generate unique values? Django 1.11.5

PS I understand, that i can set null=True and customize model's save method to add slug when saving.

Answer 1

MOST IMPORTANT: You have not good generator for unique slug, may be best way use uuid for example

import uuid

slug = models.CharField(max_length=64, blank=True, unique=True, default=uuid.uuid4)

by add-unique-fields

1. Added null=True, without default With data migration
2. Alter model with current filed description, with migrate.

example first step migration, replace YOUMODEL:

from __future__ import unicode_literals
import string
import random
from django.db import migrations, models


def id_generator():
    size=16
    chars=string.ascii_lowercase + string.digits
    return ''.join(random.choice(chars) for x in range(size))

def update_slug(pp, schema_editor):
    for instance in YOUMODEL.objects.all():
        #           ^^^^^^^
        instance.slug = id_generator()
        instance.save()


class Migration(migrations.Migration):

    operations = [
        migrations.AddField(
            model_name='YOUMODEL',
            #           ^^^^^^^
            name='slug',
            field=models.SlugField(null=True, verbose_name='URL'),
        ),
        migrations.RunPython(code=update_slug)

    ]