尝试迁移 Django 中的模型时出现值错误

Question

I am trying to run migrations on my models but keep running into a ValueError.

Here is my models.py:

class Vehicles(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    make = models.CharField(max_length=128)
    model = models.CharField(max_length=128)
    cover_image = models.ImageField(default='vehicle_cover_pics/default.jpg', upload_to='vehicle_cover_pics')

    class Meta:
        verbose_name = 'Vehicles'
        verbose_name_plural = 'Vehicles'

    def __str__(self):
        return f"{self.user.username}'s {self.model}"

def get_image_filename(instance, filename):
    id = instance.vehicle.id
    return f"vehicle_pics/{id}.jpg"

class VehicleImages(models.Model):
    vehicle = models.OneToOneField(Vehicles, on_delete=models.CASCADE)
    image = models.ImageField(upload_to=get_image_filename, default=None)

    class Meta:
        verbose_name = 'Vehicle Images'
        verbose_name_plural = 'Vehicle Images'

    def __str__(self):
        return f"{self.vehicle.user.username}'s {self.vehicle.model} Image"

And when I try to migrate the models i get the following error:

C:\Users\T Smith\Documents\Python\garage>python manage.py migrate
Operations to perform:
  Apply all migrations: accounts, admin, auth, contenttypes, home, sessions
Running migrations:
  Applying accounts.0021_auto_20200508_1328... OK

  Applying home.0002_auto_20200507_1905...Traceback (most recent call last):
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\db\models\fields\__init__.py", line 1768, in get_prep_value
    return int(value)
ValueError: invalid literal for int() with base 10: 'None'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\core\management\__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\core\management\__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\core\management\base.py", line 328, in run_from_argv
    self.execute(*args, **cmd_options)
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\core\management\base.py", line 369, in execute
    value = self.get_prep_value(value)
  File "C:\Users\T Smith\Anaconda3\lib\site-packages\django\db\models\fields\__init__.py", line 1772, in get_prep_value
    ) from e
ValueError: Field 'id' expected a number but got 'None'.

I think it has something to do with the "get_image_filename" function I'm using to tie multiple images back to one "Vehicle" instance.

Right now there is no data stored in the model so maybe it is kicking back the error when trying to run? Maybe I need to find a way for that function to only run when data is available?

I'm pretty new to this stuff so any help would be much appreciated. Thank you!

UPDATE: Here's what I believe is the initial migration file for the models. I have since changed the ForiegnKey fields to OneToOne.

import accounts.models
from django.conf import settings
from django.db import migrations, models
import django.db.models.deletion


class Migration(migrations.Migration):

    dependencies = [
        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
        ('accounts', '0011_auto_20200422_1529'),
    ]

    operations = [
        migrations.CreateModel(
            name='Vehicles',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('make', models.CharField(max_length=128)),
                ('model', models.CharField(max_length=128)),
                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL)),
            ],
        ),
        migrations.CreateModel(
            name='VehicleImages',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('image', models.ImageField(upload_to=accounts.models.get_image_filename)),
                ('vehicle', models.ForeignKey(default=None, on_delete=django.db.models.deletion.CASCADE, to='accounts.Vehicles')),
            ],
        ),
    ]

ANd here is the migration for 0021_auto_20200508_1328.py:

import accounts.models
from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('accounts', '0020_auto_20200508_1317'),
    ]

    operations = [
        migrations.AlterField(
            model_name='vehicleimages',
            name='image',
            field=models.ImageField(default=None, upload_to=accounts.models.get_image_filename),
        ),
    ]

Answer 1

You said: "Maybe I need to find a way for that function to only run when data is available?"

FOR THIS

if instance.vehicle.id is not None
   id = instance.vehicle.id
   return f"vehicle_pics/{id}.jpg"

This will serve the purpose. But if you want to initialize it anyway then could you please share the migrations file?

Answer 2

Delete all migrations and modify the the of the field vehicle to models.ForeignKey(Vehicles, on_delete= models.CASCADE). It should work.