class BaseModel(models.Model):
    id = models.UUIDField(default=uuid.uuid4, editable=False, db_index=True, unique=True, primary_key=True)
    updated_at = models.DateTimeField(db_index=True, auto_now=True)
    updated_by = models.CharField(max_length=200)
    responded_at = models.DateTimeField(db_index=True, null=True, blank=True)
    responded_by = models.CharField(max_length=200, null=True, blank=True)

from django.utils import timezone


class AutoDateTimeField(models.DateTimeField):
    def pre_save(self, model_instance, add):
        return timezone.now()

class BaseModel(models.Model):
    updated_at = models.AutoDateTimeField(default=timezone.now)
    # ...