writing django signal hook to check whether user already exists

Question

We recently switched from one LDAP system to another. Unfortunately, not only the LDAP server changed but all usernames did too.

I managed to configure django_auth_ldap to deal with two LDAP servers, however I can not prevent the creation of new users in my database.

I tried to hook up a listener to django_auth_ldap.backend.populate_user.connect but that signal gets evaluated after a user had been created.

So what's the best approach to do:

authenticate user
check if username in database
check for alternative username in database
update username if necessary (old & new user mapping found)
create new user if not found anywhere

EDIT I'm aware of signal handlers, but I don't know how (and where in the code) to solve the task of preventing duplicate user creation. Where should I hook my code up that checks for old vs new usernames?

EDIT2:

I've tried to following, but still a new_name user is being created.

# touple of old user and new user names
username_list = [('old_name', 'new_name') ]

@receiver(pre_save, sender=User)
def check_if_user_exists(sender, **kwargs):
    try:
        print "check_if_user_exists:"
        user_instance = kwargs['instance']
        print user_instance
        if any([x[1] == user_instance.username for x in username_list]):
            print "new user name found!"
            # get old username
            user = User.objects.get(username = x[0])
            user.username = user_instance.username
            return user
        else:
            print "user not found :("
    except ObjectDoesNotExist:
        print ('user not found')
        pass

Would this link help: https://docs.djangoproject.com/en/dev/ref/signals/#django.db.models.signals.pre_save ? — Henrik Andersson, Apr 15 '13 at 15:14
@limelights sure, but it doesn't help me, since it's just a link to signal docs. I need to some input regarding the implementation. — memyself, Apr 15 '13 at 15:16

Henrik Andersson · Answer 1 · 2013-04-15T15:29:41.397

0

This is how you implement a signal_handler on a pre_save. These should live in your models.py.

@receiver(pre_save, sender=MyModel)
def check_if_user_exists_based_on_whatever(sender, **kwargs):
    try:
        user = MyModel.objects.get(kwargs['instance'].<field_to_get_on_model>)
        user.username = "new_username"
        user.save()
    except ObjectDoesNotExist:
        user = MyModel.create(name="mymyself", lastname="andI")

This is just a basic example, I don't really know all of your validation logic. ^_^

edited Apr 15 '13 at 15:29

answered Apr 15 '13 at 15:23

Henrik Andersson

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This doesn't fuse with a LDAP binding but I guess you could surpass that hurdle. – Henrik Andersson Apr 15 '13 at 15:25
so instead of `MyModel` I can also use `django.contrib.auth.models.User`? do I have to return `user`? – memyself Apr 15 '13 at 15:27
Yep and Nope. You don't have to return anything. – Henrik Andersson Apr 15 '13 at 15:28
Edited code, i had 'user_id' as key in `kwargs` this was wrong, it should be `instance`. Sorry. See here what's availiable to you https://docs.djangoproject.com/en/dev/ref/signals/#pre-save – Henrik Andersson Apr 15 '13 at 15:30
I tried your code (see my EDIT #2) but I still end up with new users. – memyself Apr 15 '13 at 15:47
You are calling user.save() somewhere, thats why you get new ones. You have to raise an exception when/if you find a user in your signal. – Henrik Andersson Apr 15 '13 at 15:55
some library might be calling user.save() somewhere. but I can't control that. So how should I modify above code to detect existing users and simply change the username? – memyself Apr 15 '13 at 16:11
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/28264/discussion-between-limelights-and-memyself) – Henrik Andersson Apr 15 '13 at 16:15

score 0 · Answer 2 · answered Apr 15 '13 at 17:45

0

I ended up writing my own authentication backend, overwriting get_or_create_user.

answered Apr 15 '13 at 17:45

memyself

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writing django signal hook to check whether user already exists

2 Answers2