Question

我正在使用C＃中的JSON元素解析大型数据文件。对于某些字符串，反序列化失败，错误如下。

 Exception  = Invalid cast from 'DateTime' to 'Int64'.
 Message    = Error converting value 3/28/2172 12:00:00 AM to type 'System.Int64'.  Path 'ProductDetail.productId', line 1, position 4003."

所有字符串都没有出现错误，但似乎暗示该值被解释为DateTime值;但是，它在相关联的类中被定义为 long 。

我可以强制将值解释为长吗？

ProductDetail.productId被定义为以下类型的成员：

   public class ProductDetail
    {
        public string accreditedInvestorInd { get; set; }
        public string accrueAcreteInd { get; set; }
        public DateTime issueDate { get; set; }
        // ... truncated for simplicity

        public long productId { get; set; }

       // ... truncated for simplicity
        public string wkndHolPayInd { get; set; }
        public string zeroCouponInd { get; set; }
    }

我尝试使用转换器属性未能成功，希望强制使用不同的解释。（不确定我是否正确使用它）......

    [JsonConverter(typeof(string))]
    public long productId { get; set; }

另外，我使用的是自定义DateTime格式。

以下是我尝试反序列化的大数据文件的子集，与ProductDetail对应：

{"accrueAcreteInd":"Y","callableInd":"Y","calledInd":"N","cpnCurrency":"USD","cpnPmtFreqCode":"S","cpnRate":"2.8","curAmtOutstanding":"7825000.0","currencyCode":"USD","cusip":"3130H0AX1","datedDate":"20160303","dayCountMonthCode":"30","dayCountYearCode":"360","daysToSettle":"1","dtcEligibleInd":"Y","eomPmtInd":"N","exchange":"TRACE","fatcaCode":"1","firstCpnPmtDate":"20160901","hqlaCode":"2A","identifier":"3130H0AX1","identifierType":"cusip","inDefaultInd":"N","infoSourceCode":"R21RB","intAccrued":".91777778","intTypeCode":"FIX","is144aInd":"N","issueCountry":"US","issueDate":"20160303","issuePrice":"100.0","issuerIndustryCode":"11","issuerName":"FARMER MAC","issuerTicker":"FAMCA","lastCpnPmtDate":"20250901","lastUpdateTime":"20160830","lastUpdateTimeExt":"00:06:58","longDesc":"FAMCA 2.8 03/01/2026","maturityDate":"20260301","minDenom":"1000.0","minParAmount":"1000.0","mktSectorDes":"Govt","mtnInd":"Y","nextCallDate":"20170301","nextCallPrice":"100.0","nextCpnPmtDate":"20170301","origIssueAmt":"7825000.0","prevCpnPmtDate":"20160901","primaryIssInd":"Y","privatePlacementInd":"N","productId":"21720328","productTypeCode":"FRMNT","putableInd":"N","pxCleanInd":"Y","redempVal":"100.0","regSInd":"N","restrictedInd":"N","secHoldInd":"N","securityType":"FAMCCL","series":"NOTZ","shortDesc":"FAMCA 2.8 03/26","sinkableInd":"N","traceEligibleInd":"N","truePutInd":"N","wkndHolPayInd":"N","zeroCouponInd":"N"}

以下是我尝试反序列化子集的方法，其中Line是上面的JSON字符串：

var dateFormatSettings = new JsonSerializerSettings { DateFormatString = "yyyyMMdd" };
var detail = JsonConvert.DeserializeObject<ProductDetail>(Line, dateFormatSettings);

以下是简化JSON的完整例外：

Newtonsoft.Json.JsonSerializationException: Error converting value 3/28/2172 12:00:00 AM to type 'System.Int64'. Path 'productId', line 1, position 1117. ---> System.InvalidCastException: Invalid cast from 'DateTime' to 'Int64'.
   at System.DateTime.System.IConvertible.ToInt64(IFormatProvider provider)
   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   --- End of inner exception stack trace ---
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)

Answer 1

问题与您正在使用的具体DateFormatString有关：

var dateFormatSettings = new JsonSerializerSettings { DateFormatString = "yyyyMMdd" };

JSON没有literal syntax for dates因此，在较低级别，Json.NET使用DateFormatString设置进行一些模式匹配以识别日期字符串。很遗憾，DateFormatString yyyyMMdd设置与以下两种JSON属性匹配：

   "issueDate":"20160303", // Should deserialize to a DateTime
   "productId":"21720328", // Should deserialize to a long

因此，当第一个被正确识别为日期时，第二个也是，最终导致更高代码级别的"Invalid cast from 'DateTime' to 'Int64'."异常。它是一个边缘案例，因为对应于long成员的JSON字符串值可以解析为long和DateTime，但这可以说是Json.NET中的一个错误。

您有几个解决方法：

通过设置JsonSerializerSettings.DateParseHandling = DateParseHandling.None：
禁用自动日期识别
```
var dateFormatSettings = new JsonSerializerSettings
{
    DateParseHandling = DateParseHandling.None,
    DateFormatString = "yyyyMMdd"
};
```
尽管禁用了低级自动识别功能，但明确键入DateTime的成员仍会正确反序列化。
使用IsoDateTimeConverter { DateTimeFormat = "yyyyMMdd" }而非设置JsonSerializerSettings.DateFormatString。
```
var dateFormatSettings = new JsonSerializerSettings
{
    Converters = { new IsoDateTimeConverter { DateTimeFormat = "yyyyMMdd" } }
};
```
明确键入为DateTime的成员将使用您想要的格式字符串进行反序列化，同时保留用于低级自动识别的模式不变。

示例fiddle重现问题并演示两个解决方法。

＆＃34;来自＆＃39; DateTime＆＃39;的无效演员表到＆＃39; Int64＆＃39;。在反序列化JSON字符串时

1 个答案: