使用方法 'build_standard_field(self, field_name, model_field)' 来克服错误 [<class 'decimal.InvalidOperation'>]

Question

我正在编写一个 Django Rest 框架，我想使用 generics.CreateAPIView 在我的数据库中创建一个操作。
我的 models.py：

class User(AbstractBaseUser, PermissionsMixin):
    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    email = models.EmailField("Email Address", unique=True)
    first_name = models.CharField("First Name", max_length=150)
    last_name = models.CharField("Last Name", max_length=150)
    mobile = models.CharField("Mobile Number", max_length=150, blank=True)
    balance = models.DecimalField(max_digits=9, decimal_places=2, default=0.0, verbose_name=("Balance"))
    created_at = models.DateTimeField("Created at", auto_now_add=True, editable=False)


class Operation(models.Model):
    sender = models.ForeignKey("User", related_name=("Sender"), on_delete=models.CASCADE)
    receiver = models.ForeignKey("User", related_name=("Receiver"), on_delete=models.CASCADE)
    amount = models.DecimalField(max_digits=9, decimal_places=2, default=0.0, verbose_name=("Amount"))
    created_at = models.DateTimeField("Created at", auto_now_add=True, editable=False)

我想在创建操作时发送 uuid 值并使用视图在后端处理用户过滤器。 所以我在序列化器中添加了额外的字段：

class OperationCreateSerializer(serializers.ModelSerializer):
    sender_uuid = serializers.UUIDField(format='hex_verbose')
    receiver_uuid = serializers.UUIDField(format='hex_verbose')
    amount = serializers.DecimalField(max_digits=9, decimal_places=2, coerce_to_string=False)

    class Meta:
        model = Operation
        fields = ["sender_uuid", "receiver_uuid", "amount"]
        write_only_fields = ["sender_uuid", "receiver_uuid"]


class OperationListSerializer(serializers.ModelSerializer):
    
    class Meta:
        model = Operation
        fields = ["sender", "receiver", "amount"]

问题是当我尝试创建 transfert 操作时，视图中的字段 'amount' 出现错误 [<class 'decimal.InvalidOperation'>]。 我认为我使用的逻辑是：

class TransferView(generics.CreateAPIView):
    serializer_class = OperationCreateSerializer
    queryset = Operation.objects.all()

    def create(self, request, *args, **kwargs):
        serializer = OperationCreateSerializer(data=request.data)
        if serializer.is_valid(raise_exception=True):
            print(serializer.validated_data.get('amount'))
        if serializer.is_valid(raise_exception=True):
            with transaction.atomic():
                sender = User.objects.filter(uuid=serializer.validated_data.get('sender_uuid'))
                if sender and sender[0].balance >= serializer.validated_data.get('amount'):
                    User.objects.filter(uuid=serializer.validated_data.get('sender_uuid')).update(balance=F('balance') - serializer.validated_data.get('amount', 0))
                    User.objects.filter(uuid=serializer.validated_data.get('receiver_uuid')).update(balance=F('balance') + serializer.validated_data.get('amount', None))
                    serializer.save(sender=User.objects.get(uuid=serializer.validated_data.get('sender_uuid')), receiver=User.objects.get(uuid=serializer.validated_data.get('receiver_uuid')))
                    return Response({'message': 'transfer done successfully'}, status=status.HTTP_201_OK)
                else:
                    return Response({'message': 'insufficient balance'}, status=status.HTTP_400_BAD_REQUEST)
        return Response(status=status.HTTP_400_BAD_REQUEST)


class TransactionViewSet(generics.ListAPIView):
    permission_classes = (IsAuthenticated,)
    serializer_class = OperationListSerializer
    queryset = Operation.objects.all()

    def get_queryset(self, **kwargs):
        """
        Restricting the returned purchased Operations to a given a date range query 
        parameter in the URL.
        """
        start = self.request.query_params.get('start_date')
        end = self.request.query_params.get('end_date')
        try:
            queryset = self.queryset.filter(Q(created_at__range=[start, end]))
            return queryset
        except Operation.DoesNotExist:
            raise Http404

我不知道该字段的 Decimale 值有什么问题，我发现有办法映射额外字段 fields = ["sender_uuid", "receiver_uuid"] 我用来将 uuid 值发送到后端使用方法在模型fields = ["sender", "receiver"] 中的适当字段

> build_standard_field(self, field_name, model_field) 我不知道如何使用此方法以及为什么在尝试创建实例时出现错误。

编辑：
这是我得到的错误：

Internal Server Error: /v1/api/transfert/
Traceback (most recent call last):
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/rest_framework/generics.py", line 190, in post
    return self.create(request, *args, **kwargs)
  File "/home/mohammed/Projects/PaymentSystem/payment_api/account/views.py", line 30, in create
    serializer.save(sender=User.objects.get(uuid=serializer.validated_data.get('sender_uuid')), receiver=User.objects.get(uuid=serializer.validated_data.get('receiver_uuid')), amount=decimal.Decimal(serializer.validated_data.get('amount')))
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/query.py", line 431, in get
    num = len(clone)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/query.py", line 262, in __len__
    self._fetch_all()
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/query.py", line 1324, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/query.py", line 68, in __iter__
    for row in compiler.results_iter(results):
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/models/sql/compiler.py", line 1122, in apply_converters
    value = converter(value, expression, connection)
  File "/home/mohammed/Projects/PaymentSystem/paymentsys/lib/python3.7/site-packages/django/db/backends/sqlite3/operations.py", line 313, in converter
    return create_decimal(value).quantize(quantize_value, context=expression.output_field.context)
decimal.InvalidOperation: [<class 'decimal.InvalidOperation'>]
[03/Jan/2022 15:58:16] "POST /v1/api/transfert/ HTTP/1.1" 500 145513

Answer 1

第一个可能导致错误的原因是您的DecimalFields 配置中的default=0.0。必须是default=Decimal(0)；在某些版本的 Django 中，它可能会引起麻烦。

此外，当您的数据无法转换为Decimal 时，通常会发生此错误，尤其是当max_digits 数字不足以满足您的值时。

来自Django docs：

DecimalField.max_digits 数字中允许的最大位数。请注意，此数字必须大于或等于 decimal_places。

DecimalField.decimal_places 与数字一起存储的小数位数。

所以如果你需要在DecimalField中存储1_000_000_000.00，你必须配置它max_digits=11, decimal_places=2，而不是max_digits=9, decimal_places=2。