JSON反序列化为DataTable遇格式错误，求排查JSON字符串问题

问题详情 #

尝试将JSON字符串反序列化为DataTable时触发格式错误，相关代码、JSON字符串及报错信息如下：

C#代码 #

string str = "{\"Arg1\":\"Arg1Value\",\"Arg2\":\"Arg2Value\",\"DataArray\":[{\"Id\": \"2222\",\"VehicleNo\": \"234354\",\"Amount\":\"1000\"},{\"Id\":\"2226\",\"VehicleNo\":\"2343\",\"Amount\":\"2000\"}]}";
DataTable data = Newtonsoft.Json.JsonConvert.DeserializeObject<DataTable>(str);

原始报错信息 #

Unexpected JSON token when reading DataTable. Expected StartArray, got StartObject. Path '', line 1, position 1."Data":null,"InnerException":null,"HelpURL":null,"StackTraceString":" at Newtonsoft.Json.Converters.DataTableConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)\r\n at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)

报错信息翻译 #

读取DataTable时遇到意外的JSON令牌。期望数组起始符[，却得到对象起始符{。路径''，第1行，第1位。"Data":null,"InnerException":null,"HelpURL":null,"StackTraceString":" 在Newtonsoft.Json.Converters.DataTableConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)\r\n 在Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)\r\n 在Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)\r\n 在Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)

问题根源 #

Newtonsoft.Json的DataTableConverter要求反序列化为DataTable的JSON必须以数组（[]）作为根节点，但你提供的JSON根节点是包含Arg1、Arg2、DataArray三个属性的对象（{}），不符合DataTable的反序列化规则。实际对应DataTable数据的是对象内部的DataArray数组。

解决办法 #

方法1：提取DataArray部分反序列化 #

先将整个JSON反序列化为临时对象，提取DataArray后再转为DataTable：

var tempObj = Newtonsoft.Json.JsonConvert.DeserializeAnonymousType(str, new { DataArray = default(List<object>) });
DataTable data = Newtonsoft.Json.JsonConvert.DeserializeObject<DataTable>(Newtonsoft.Json.JsonConvert.SerializeObject(tempObj.DataArray));

方法2：修改JSON结构（若允许调整输入） #

直接将JSON根节点替换为DataArray的数组内容，去掉外层对象：

[{"Id": "2222","VehicleNo": "234354","Amount":"1000"},{"Id":"2226","VehicleNo":"2343","Amount":"2000"}]

之后直接执行反序列化：

string str = "[{\"Id\": \"2222\",\"VehicleNo\": \"234354\",\"Amount\":\"1000\"},{\"Id\":\"2226\",\"VehicleNo\":\"2343\",\"Amount\":\"2000\"}]";
DataTable data = Newtonsoft.Json.JsonConvert.DeserializeObject<DataTable>(str);

方法3：自定义类映射转换 #

定义匹配JSON结构的类，先反序列化为类实例，再将DataArray转换为DataTable：

public class RootModel
{
    public string Arg1 { get; set; }
    public string Arg2 { get; set; }
    public List<DataItem> DataArray { get; set; }
}

public class DataItem
{
    public string Id { get; set; }
    public string VehicleNo { get; set; }
    public string Amount { get; set; }
}

// 反序列化代码
var root = Newtonsoft.Json.JsonConvert.DeserializeObject<RootModel>(str);
DataTable data = Newtonsoft.Json.JsonConvert.DeserializeObject<DataTable>(Newtonsoft.Json.JsonConvert.SerializeObject(root.DataArray));

内容的提问来源于stack exchange，提问作者AMDI