DRF创建用户时出现username字段过长错误的排查求助

Let's break down the root causes of this error and walk through the fixes step by step:

1. Critical Issue: Accessing Serializer Fields Instead of Validated Data #

The biggest mistake is in your view code—you're passing serializer field instances (not the actual username/password values from the request) to create_user. The string representation of a CharField instance is way longer than 20 characters, which directly causes the DataError when inserting into the username column.

Fix the View (views.py) #

class MyUserCreate(APIView):
    """ Creates the user. """
    def post(self, request, format='json'):
        serializer = MyUserSerializer(data=request.data)
        if serializer.is_valid():
            # Use validated_data to get the actual request values
            user = MyUser.objects.create_user(
                username=serializer.validated_data['username'],
                password=serializer.validated_data['password']
            )
            # No need for redundant user check—create_user returns the user
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

2. Syntax Error: Trailing Comma on Serializer Username Field #

The trailing comma after your username field definition turns it into a tuple instead of a valid CharField instance. This breaks validation and leads to unexpected behavior.

3. Misused make_password in Serializer #

Wrapping make_password around the password field definition hashes the field object itself (not the user's input password) when the serializer loads. Your model's create_user method already handles password hashing via set_password, so this is redundant and incorrect.

Fix the Serializer (serializers.py) #

class MyUserSerializer(serializers.ModelSerializer):
    username = serializers.CharField(
        required=True,
        validators=[UniqueValidator(queryset=MyUser.objects.all())],
        min_length=5, max_length=20
    )  # Removed trailing comma
    password = serializers.CharField(
        write_only=True, required=True, max_length=256
    )  # Removed make_password wrapper

    class Meta:
        model = MyUser
        fields = ('username', 'password')

    # Override create to use the model's create_user method
    def create(self, validated_data):
        return MyUser.objects.create_user(
            username=validated_data['username'],
            password=validated_data['password']
        )

4. Verify Model Logic (Already Correct) #

Your MyUser model and MyUserManager are correctly set up—create_user uses set_password to hash the password, and the username field has a valid max length of 20. No changes needed here.

Why This Works #

After applying these fixes:

• The view correctly pulls the actual username/password values from the validated request data
• The serializer properly validates the username length (5-20 characters) before passing it to the model
• The password is hashed correctly by the model's create_user method
• Your POST request {"username": "tiagoperes", "password": "test"} will now insert a valid username (10 characters, well under the 20 limit) into the database.

内容的提问来源于stack exchange，提问作者Tiago Peres