django - 如果未明确指定，则为 DRF ModelSerializer 中的 "user with this username already exists"

Question

虽然我知道如何解决，但我正在尝试理解为什么会出现此错误。只是想更好地理解 DRF 和 Django。

这种格式的JSON来自FE:

{
  "username": "username_here",
  "password": "password_here"
}

我的看法是:

class UserSigninTokenAPIView(APIView):
    permission_classes = [AllowAny]
    serializer_class = UserSigninTokenSerializer

    def post(self, request):
        data = request.data
        serializer = UserSigninTokenSerializer(data=data)
        if serializer.is_valid(raise_exception=True):
            new_data = serializer.data
            return Response(new_data, status=HTTP_200_OK)
        return Response(serializer.errors, status=HTTP_400_BAD_REQUEST)

它使用这个序列化器:

class UserSigninTokenSerializer(ModelSerializer):
    username = CharField()

    class Meta:
        model = USERS
        fields = [
            'username',
            'password',
            'id'
        ]

    def validate(self, data):
        username = data['username']
        password = data['password']
        user_qs = USERS.objects.filter(username__iexact=username)
        if user_qs.exists() and user_qs.count() == 1:
            user_obj = user_qs.first()
            password_passes = user_obj.check_password(password)
            if password_passes:
                """
                A number of checks here I removed to keep this clean,
                otherwise would just use /api/token/ to get a token.
                I want user checks to pass before issuing a token,
                because having the token is what indicates they are 
                logged in successfully.
                """
                token = RefreshToken.for_user(user_obj)
                return {
                    'refresh': str(token),
                    'access': str(token.access_token)
                }
            else:
                Services.user_attempts(user_obj)
        raise ValidationError({'error': '''
            The credentials provided are invalid.
            <br>Please verify the username and password are correct.
        '''})

username = CharField() 对我来说似乎是多余的。 documentation说:

The ModelSerializer class provides a shortcut that lets you automatically create a Serializer class with fields that correspond to the Model fields.

我将其解释为仅在 class Meta: 中指定 field = [] 就足以反序列化 JSON。

但是，当我删除 username = CharField() 时，我得到:

{
    "username": [
        "user with this username already exists."
    ]
}

documentation对于明确的规范说:

You can add extra fields to a ModelSerializer or override the default fields by declaring fields on the class, just as you would for a Serializer class.

这听起来是可选的，但显然必须指定它。

如果有人不介意解释，我在这里错过了什么？

Answer 1

您正在对您的模型使用 ModelSerializer 并且请求是 POST，难怪您为什么会得到这个。

ModelSerializer 用于为 CRUD 操作提供快速的标准序列化，因此当您的请求是 POST 时，您的序列化程序将假定您正在使用该请求创建一个新用户Users 模型的数据，因此将应用创建验证，并且由于用户名是唯一的...，剩下的就是故事了。

尝试使用基本的序列化器，因为你只想读取数据，这样会更简单