PositiveBigAutoFileld & PositiveBigIntegerField. Auto Increment Big Integer in Django (mysql)

__init__.py

from django.db.models import fields

__all__ = [
    'PositiveBigAutoField', 'PositiveBigIntegerField',
]


class PositiveBigAutoField(fields.AutoField):
    def db_type(self, connection):
        if 'mysql' in connection.__class__.__module__:
            return 'bigint unsigned AUTO_INCREMENT'

        return super().db_type(connection)

    def rel_db_type(self, connection):
        return PositiveBigIntegerField().db_type(connection=connection)


class PositiveBigIntegerField(fields.BigIntegerField):
    def db_type(self, connection):
        if 'mysql' in connection.__class__.__module__:
            return 'bigint unsigned'

        return super().db_type(connection)

    def db_check(self, connection):
        data = self.db_type_parameters(connection)

        if 'oracle' in connection.__class__.__module__:
            return '%(qn_column)s >= 0' % data
        elif 'postgresql' in connection.__class__.__module__:
            return '"%(column)s" >= 0' % data
        elif 'sqlite3' in connection.__class__.__module__:
            return '"%(column)s" >= 0' % data

        return super().db_check(connection)

    def formfield(self, **kwargs):
        return super().formfield(**{
            'min_value': 0,
            **kwargs,
        })

You can put that code anywhere, but for me ideally I would like to put that in:

---- app
-------- __init__.py
-------- db
------------ __init__.py
------------ models
---------------- __init__.py
---------------- fields
-------------------- __init__.py <-- here

Then, you can use it like so:

from .db.models import fields as common_fields
from django.db import models
from django.contrib.auth.models import AbstractBaseUser

class User(AbstractBaseUser):
    id = common_fields.PositiveBigAutoField(
        auto_created=True,
        primary_key=True,
        serialize=False,
        verbose_name='ID'
    )