JSON 值有时是字符串，有时是对象

Question

我有一些可以有两种不同格式的 JSON。有时location 值是一个字符串，有时它是一个对象。这是第一种格式的示例：

{
  "result": [
    {
      "upon_approval": "Proceed to Next Task",
      "location": "",
      "expected_start": ""
    }
  ]
}

为此的类定义：

public class Result
{
    public string upon_approval { get; set; }
    public string location { get; set; }
    public string expected_start { get; set; }
}

public class RootObject
{
    public List<Result> result { get; set; }
}

这是第二种格式的 JSON：

{
  "result": [
    {
      "upon_approval": "Proceed to Next Task",
      "location": {
        "display_value": "Corp-HQR",
        "link": "https://satellite.service-now.com/api/now/table/cmn_location/4a2cf91b13f2de00322dd4a76144b090"
      },
      "expected_start": ""
    }
  ]
}

为此的类定义：

public class Location
{
    public string display_value { get; set; }
    public string link { get; set; }
}

public class Result
{
    public string upon_approval { get; set; }
    public Location location { get; set; }
    public string expected_start { get; set; }
}

public class RootObject
{
    public List<Result> result { get; set; }
}

在反序列化时，如果 JSON 格式与我的类不匹配，我会收到错误消息，但我不知道要使用哪些类，因为 JSON 格式会发生变化。那么如何动态地让这两种 JSON 格式反序列化为一组类呢？

这就是我现在反序列化的方式：

JavaScriptSerializer ser = new JavaScriptSerializer();
ser.MaxJsonLength = 2147483647;
RootObject ro = ser.Deserialize<RootObject>(responseValue);

Answer 1

要解决这个问题，您需要创建一个自定义 JavaScriptConverter 类并将其注册到序列化程序。序列化器会将result 数据加载到Dictionary<string, object> 中，然后交给转换器，您可以在其中检查内容并将其转换为可用对象。简而言之，这将允许您将第二组类用于两种 JSON 格式。

这是转换器的代码：

class ResultConverter : JavaScriptConverter
{
    public override IEnumerable<Type> SupportedTypes
    {
        get { return new List<Type> { typeof(Result) }; }
    }

    public override object Deserialize(IDictionary<string, object> dict, Type type, JavaScriptSerializer serializer)
    {
        Result result = new Result();
        result.upon_approval = GetValue<string>(dict, "upon_approval");
        var locDict = GetValue<IDictionary<string, object>>(dict, "location");
        if (locDict != null)
        {
            Location loc = new Location();
            loc.display_value = GetValue<string>(locDict, "display_value");
            loc.link = GetValue<string>(locDict, "link");
            result.location = loc;
        }
        result.expected_start = GetValue<string>(dict, "expected_start");
        return result;
    }

    private T GetValue<T>(IDictionary<string, object> dict, string key)
    {
        object value = null;
        dict.TryGetValue(key, out value);
        return value != null && typeof(T).IsAssignableFrom(value.GetType()) ? (T)value : default(T);
    }

    public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

然后像这样使用它：

var ser = new JavaScriptSerializer();
ser.MaxJsonLength = 2147483647;
ser.RegisterConverters(new List<JavaScriptConverter> { new ResultConverter() });
RootObject ro = serializer.Deserialize<RootObject>(responseValue);

这是一个简短的演示：

class Program
{
    static void Main(string[] args)
    {
        string json = @"
        {
          ""result"": [
            {
              ""upon_approval"": ""Proceed to Next Task"",
              ""location"": {
                ""display_value"": ""Corp-HQR"",
                ""link"": ""https://satellite.service-now.com/api/now/table/cmn_location/4a2cf91b13f2de00322dd4a76144b090""
              },
              ""expected_start"": """"
            }
          ]
        }";

        DeserializeAndDump(json);
        Console.WriteLine(new string('-', 40));

        json = @"
        {
          ""result"": [
            {
              ""upon_approval"": ""Proceed to Next Task"",
              ""location"": """",
              ""expected_start"": """"
            }
          ]
        }";

        DeserializeAndDump(json);

    }

    private static void DeserializeAndDump(string json)
    {
        var serializer = new JavaScriptSerializer();
        serializer.RegisterConverters(new List<JavaScriptConverter> { new ResultConverter() });
        RootObject obj = serializer.Deserialize<RootObject>(json);

        foreach (var result in obj.result)
        {
            Console.WriteLine("upon_approval: " + result.upon_approval);
            if (result.location != null)
            {
                Console.WriteLine("location display_value: " + result.location.display_value);
                Console.WriteLine("location link: " + result.location.link);
            }
            else
                Console.WriteLine("(no location)");
        }
    }
}

public class RootObject
{
    public List<Result> result { get; set; }
}

public class Result
{
    public string upon_approval { get; set; }
    public Location location { get; set; }
    public string expected_start { get; set; }
}

public class Location
{
    public string display_value { get; set; }
    public string link { get; set; }
}

输出：

upon_approval: Proceed to Next Task
location display_value: Corp-HQR
location link: https://satellite.service-now.com/api/now/table/cmn_location/4a2cf91b13f2de00322dd4a76144b090
----------------------------------------
upon_approval: Proceed to Next Task
(no location)