In a loop and automatically, that is, I always check all users once every 10 minutes, and I may need to update a bool field from them
How can I not change my current field when I update that bool field ?

```
class Client(models.Model):
    user = models.ForeignKey ... 
    last_activity = models.DateTimeField(_("Last Activity"), auto_now=True)
    joined = models.BooleanField(_("Joined in Default Channel"), default = False)
    ...
    ... 

```

i want to update `joined` field without change `last_activity`.

how can i do?