class SerialField(models.Field):
    description = _("BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE")

    empty_strings_allowed = False

    default_error_messages = {
        'invalid': _("'%(value)s' value must be an integer."),
    }

    def __init__(self, *args, **kwargs):
        kwargs['blank'] = True
        super().__init__(*args, **kwargs)

    def db_type(self, connection):
        return 'serial'

from .fields import SerialField

class MyModel(models.Model):
    uuid = models.UUIDField(
        verbose_name=_("UUID Identifier"),
        primary_key=True,
        default=uuid.uuid4,
        editable=False,
        help_text=_("Requried, PrimaryKey none-editable"),
        db_index=True,
    )
    number = SerialField(
        primary_key=False,
        editable=False,
        help_text=_("Auto Increment Number"),
        verbose_name=_("Number"),
        #null=True
    )

def forwards(apps, schema_editor):
    if schema_editor.connection.alias == 'default':
        return migrations.RunSQL(
            "ALTER SEQUENCE app_name_mymodel_number_seq RESTART WITH 100000"
        )


class Migration(migrations.Migration):

    dependencies = [
        ('activities', '0001_initial'),
    ]

    operations = [
        migrations.RunPython(forwards)
    ]