如何使用Newtonsoft JSON.NET 将JSON反序列化为IEnumerable<BaseType>

Question

给定此JSON:

[
  {
    "$id": "1",
    "$type": "MyAssembly.ClassA, MyAssembly",
    "Email": "[e-mail]",
  },
  {
    "$id": "2",
    "$type": "MyAssembly.ClassB, MyAssembly",
    "Email": "[e-mail]",
  }
]

以及这些类别：

public abstract class BaseClass
{
    public string Email;
}
public class ClassA : BaseClass
{
}
public class ClassB : BaseClass
{
}

如何将JSON反序列化为：

IEnumerable<BaseClass> deserialized;

我不能使用JsonConvert.Deserialize<IEnumerable<BaseClass>>()，因为它抱怨BaseClass是抽象的。

Answer 1

您需要：

JsonSerializerSettings settings = new JsonSerializerSettings
{
    TypeNameHandling = TypeNameHandling.All
};
string strJson = JsonConvert.SerializeObject(instance, settings);

所以JSON看起来是这样的：

{
  "$type": "System.Collections.Generic.List`1[[MyAssembly.BaseClass, MyAssembly]], mscorlib",
  "$values": [
    {
      "$id": "1",
      "$type": "MyAssembly.ClassA, MyAssembly",
      "Email": "[e-mail]",
    },
    {
      "$id": "2",
      "$type": "MyAssembly.ClassB, MyAssembly",
      "Email": "[e-mail]",
    }
  ]
}

然后你可以反序列化它：

BaseClass obj = JsonConvert.DeserializeObject<BaseClass>(strJson, settings);

文档：TypeNameHandling设置

Answer 2

这里有一种不用在json中填充$type的方法。

Json转换器：

public class FooConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(BaseFoo));
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject jo = JObject.Load(reader);
        if (jo["FooBarBuzz"].Value<string>() == "A")
            return jo.ToObject<AFoo>(serializer);
        if (jo["FooBarBuzz"].Value<string>() == "B")
            return jo.ToObject<BFoo>(serializer);
        return null;
    }
    public override bool CanWrite
    {
        get { return false; }
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

使用它：

var test = JsonConvert.DeserializeObject<List<BaseFoo>>(result, new JsonSerializerSettings() 
{ 
    Converters = { new FooConverter() }
});

从这里获取

Answer 3

在反序列化时使用以下JsonSerializerSettings构造：

new JsonSerializerSettings()
{
    TypeNameHandling = TypeNameHandling.Objects
})

Answer 4

您也可以将可枚举对象包装在类中：

class Wrapper
{
    IEnumerable<BaseClass> classes;
}

然后对此进行序列化和反序列化。

Answer 5

由于我只需要一个特定基类的单边序列化程序（使API返回派生类属性），我提出了当前的解决方案

public class CustomConverter : JsonConverter<BaseClass>
{
    private readonly JsonSerializerOptions _serializerOptions;
    public CustomConverter()
    {
        _serializerOptions = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            IgnoreNullValues = true,
        };
    }
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(BaseClass));
    }
    public override BaseClass Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
    public override void Write(Utf8JsonWriter writer, BaseClass value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(JsonSerializer.SerializeToUtf8Bytes(value, value.GetType(), _serializerOptions));
    }
}