Django REST Framework: force lowercase username - django

Question

I am just starting to play around with Django REST Framework for a side project, and I am trying to force all usernames to be lowercase (since by default they are case sensitive and I don't want people to have usernames like kevin and Kevin for example).
This is the code I am using to create a user:
# The serializer
class UserSerializer(serializers.ModelSerializer):
password = serializers.CharField(write_only=True)
token = serializers.SerializerMethodField()
def create(self, validated_data):
user = get_user_model().objects.create(**validated_data)
user.set_password(validated_data['password'])
user.save()
return user
def get_token(self, user):
token = Token.objects.create(user=user)
return token.key
class Meta:
model = get_user_model()
fields = ('username', 'first_name', 'last_name', 'email', 'password', 'token')
# The View
class RegisterUserView(CreateAPIView):
model = User
serializer_class = UserSerializer
permission_classes = (permissions.AllowAny, )
# And the URL pattern
urlpatterns = [
path(r'user/register/', RegisterUserView.as_view()),
]
So the user can create a new account by posting at least a username and password to user/register, and in the response he'll get the full user object (with first name, last name, email and the auth token). This works.
However, I am struggling with forcing lowercase usernames. For example when I add something like validated_data['username'] = validated_data['username'].lower() to the create function in the serializer, the server simply generates an error 500 "UNIQUE constraint failed: auth_user.username" when trying to create a user with the same username (but different case). That's of course not ideal, that error 500.
I've found some suggestions to add a custom user manager, something like this:
lass MyUserManager(BaseUserManager):
def get_by_natural_key(self, username):
return self.get(username__iexact=username)
But that didn't do anything either, after hooking it up via a custom user class and adding to the settings file. I could still create users with capitals in their username.
What's the simplest solution to get this to simply work?

Answer 1

If you're using a custom user model and want this enforced throughout Django, you can create a custom validator. For example, create a validators.py as a sibling to the models.py which contains your custom user model:
from django.core import validators
from django.utils.deconstruct import deconstructible
from django.utils.translation import gettext_lazy as _
#deconstructible
class MyUsernameValidator(validators.RegexValidator):
"""
Validator for usernames.
- Only ASCII lowercase letters, numbers and underscore are supported.
- Must start with a letter.
"""
regex = r'^[a-z][a-z0-9_]+$'
message = _(
'Enter a valid username. This value may contain only lowercase ASCII letters, '
'numbers, and underscores. Must start with a letter.'
)
flags = 0
Then in your custom user model, include:
from .validators import MyUsernameValidator
...
class User(AbstractBaseUser, PermissionsMixin):
EMAIL_FIELD = 'email'
USERNAME_FIELD = 'username'
REQUIRED_FIELDS = [
'first_name', 'last_name', 'email',
]
username = models.CharField(
max_length=16,
unique=True,
help_text=_(
'Required. 16 characters or fewer. Lowercase letters, digits _ only; must start with a letter.'
),
validators=[MyUsernameValidator()],
error_messages={
'unique': _("A user with that username already exists."),
},
)
There are some slightly simpler methods, but this will enforce it through Django, as long as you stick to the ORM. Good luck!

Answer 2

Probably the reason you are getting "UNIQUE constraint failed: auth_user.username" error is because username validation is run on unprocessed version of the username (i.e with uppercase letters), but when inserting you are trying to create a user with username converted to lowercase. To exemplify, let's say you have a user in the db with the following username:
my_username
Then you are trying to create a user with the following username:
My_Username
This passes validation because there is no user in the db with username "My_Username", but while creating, you are trying to create a user with username "my_username", which exists in the database, so you are getting an IntegrityError.
There are many ways to solve this problem, you can modify the username before passing it to the serializer, so in the serializer context username will always be lowercase. You can also use a custom ModelManager as you tried already, but you'd need to convert the uesrname to lowercase in the manager before saving. Either way, you need to validate your data with the correct version of the username, to do this you can add a validation to your serializer like this:
class UserSerializer(serializers.ModelSerializer):
...
validate_username(self, value):
try:
get_user_model().objects.get(username=value.lower())
except ObjectDoesNotExist:
# Good to go
pass
else:
# Username in use
raise serializers.ValidationError(...)
return value