[Django]-Checking if username exists in Django

by

32👍

✅

When ModelForms are bound to a model object, they have an attribute called ‘instance’, which is the model object itself. In your view, when request.method == 'POST', you’re probably creating the form instance like this:

form = ChangeNameForm(request.POST, instance=request.user)

If that’s the case, you can access the logged user from the form methods, and your validation method can be something like this:

def clean_username(self):
    username = self.cleaned_data['username']
    try:
        user = User.objects.exclude(pk=self.instance.pk).get(username=username)
    except User.DoesNotExist:
        return username
    raise forms.ValidationError(u'Username "%s" is already in use.' % username)

Consider using the .exists method, for it issues a faster query to your database than if you try to retrieve all the user information with the .get method. And the code gets a little cleaner too:

def clean_username(self):
    username = self.cleaned_data['username']
    if User.objects.exclude(pk=self.instance.pk).filter(username=username).exists():
        raise forms.ValidationError(u'Username "%s" is already in use.' % username)
    return username

Optionally, you can also follow these guidelines when raising the ValidationError.

I can’t test this code right now, so I apologize if there’s anything wrong.

👤Victor Silva

8👍

You can write function to check the username if exists like this:

@ggorlen, thanks! Update:

from django.contrib.auth.models import User

def username_exists(username):
    return User.objects.filter(username=username).exists()

from django.contrib.auth.models import User

def username_exists(username):
    if User.objects.filter(username=username).exists():
        return True
    
    return False
👤Allen Sun

0👍

This is how I managed to make it work (assuming you have a logged in user):

forms.py

from django.contrib.auth.forms import UserChangeForm
from django.contrib.auth.models import User

class MyUserChangeForm(UserChangeForm):
    def __init__(self, *args, **kwargs):
        super(MyUserChangeForm, self).__init__(*args, **kwargs)
        del self.fields['password']

    class Meta:
        model = User
        fields = ('username', 'first_name')

views.py

def home(request):
    if request.method == 'POST':
        form = MyUserChangeForm(request.POST, instance=request.user)
        if form.is_valid():
            form.save()
    else:
        form = MyUserChangeForm(instance=request.user)

    return render(request, 'change_user.html', {"form": form})
👤mariodev

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