Automatically create username in User model in Django based on other fields

Question

I have been searching for best practice, but I did not found it. I was even unable to find solution I need used by anyone else.

I need to generate username of the user based on his other data (first name & last name), optionally appending integer at the end, until I get the unique username.

I strongly prefer doing that in model. Is there some standard way to do that? Or is it only appropriate in forms? I have been researching overloading of various User model methods, as well as signals, and did not find any proper place I could add it.

Nansen

Answer 1

One possible solution could be through pre_save signal.

def my_callback(sender, **kwargs):
    obj = kwargs['instance'] 
    if not obj.id:
       username = get_unique_username(obj) # method that combines first name and last name then query on User model, if record found, will append integer 1 and then query again, until found unique username
       obj.username = username
pre_save.connect(my_callback, sender=User)

Samira

I was thinking about using that, but I am concerned with what forms will actually do with that. Forms validate the input before making call to save(), so the field would be treated as invalid. Btw. obj.save() will also call pre_save signal, so I you should probably remove that (or replace with something else you had in mind). – Nansen

Your solution works, but not always (if validation is handled before save, we are out of luck) and needs adjustments (removal of obj.save(), and get_unique_username should also work if we are updating existing model). In general I think there is no better way to do that, so your answer is acceptable. Thanks. – Nansen

Yes, now it is better (I use obj.pk instead of obj.id just for consistency with different models, where I have primary keys different than id; I also check if username is defined and not empty). I have already accepted your answer, now I can upvote it also :) +1 – Nansen