Disallow user's last name in username

Question

Using the Django framework, I've built a user-based web application. After some time, my client requested that the application disallow creating usernames that contain users' last names.

I have two questions:

1. Is it possible to do this reliably, always catching someone trying to register a username containing their last name, which is also present as a sign-up field? (My understanding and experience is that users can easily subvert this and still make the username look like their last name just by adding special characters or integers.)

2. What would be the best way to do this?

Answer 1

I don't think you can accomplish this withoud knowing their last name first. For example if I can make my username:

joevasquez OR jvasquez OR vasquezj OR vasquez...

There are no rules on what constitutes someome's last name. What if someone's last name is joe? It's not like filtering swearwords.

What is the reason behind this request? If it's privacy you can inform the user, but I don't think you can stop people from using their last names.

Answer 2

Try creating a custom validation rule. The function (which would be a member method of a subclass of django.forms.Field) might look something like this:

def validate(self, value):
    if len(re.findall(self.lastname,value)) > 0:
        raise forms.ValidationError('Your username may not contain your last name.')
    return value

Answer 3

You can simply have your app autogenerate the usernames? Or use email as username?