C# 序列化通用包装类

Question

我正在尝试为

Optional

包装类实现 JSON 序列化。我希望序列化类似于可为 null 的类型，所以：

"myOptional": null

对于空，并且

"myOptional": 2

或

"myOptional": { . . . }

对于物体。

这很好，直到我到达一个包装的对象，我不知道如何告诉序列化器“像平常一样序列化这个对象”。微软文档让我相信我必须实现

JsonConverterFactory

，但我不知道如何告诉作者自动序列化内部对象。

public class OptionalTypeJsonConverterFactory : JsonConverterFactory
{
    public override bool CanConvert(Type typeToConvert)
    {
        return typeToConvert
            .GetGenericArguments()[0].IsClass;
    }

    public override JsonConverter CreateConverter(
        Type type,
        JsonSerializerOptions options
    )
    {
        return (JsonConverter)Activator.CreateInstance(
            type: typeof(OptionalJsonConverter<>).MakeGenericType(type.GenericTypeArguments[0]),
            bindingAttr: BindingFlags.Instance | BindingFlags.Public,
            binder: null,
            args: new object[] { options },
            culture: null
        )!;
    }

    private class OptionalJsonConverter<T> : JsonConverter<Optional<T>>
        where T : struct
    {
        public OptionalJsonConverter(JsonSerializerOptions options) { }

        public override Optional<T>? Read(
            ref Utf8JsonReader reader,
            Type typeToConvert,
            JsonSerializerOptions options
        )
        {
            throw new NotImplementedException();
        }

        public override void Write(
            Utf8JsonWriter writer,
            Optional<T> optional,
            JsonSerializerOptions options
        )
        {
            if (optional.IsNone())
            {
                writer.WriteNullValue();
            }
            else
            {
                // don't know what to put here. I want to serialize objects as if the wrapper was never there.
            }
        }
    }
}

我应该如何实现这一目标？ 举个例子，如果

Optional<T>

有

T = MyClass

并且

MyClass

是

{
  public int ID { get; set; } = 2
  public string Name { get; set; } = "myname"
}

然后我希望将其序列化为

"optionalofMyClass": 
{
  "ID": 2,
  "Name": "myname"
}

Answer 1

如果我理解你的问题，你想序列化你的对象，无论它是否有值。如果它没有值，它应该显示为 null，当它有值时，它应该显示为嵌套的 json 结构。我尝试使用下面的代码

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

public class Program
{
    public static void Main()
    {
        Person p1 = new Person {Id = 1, Name = "User1"};
        var output1 = new Wrapper<Person>(p1);
        Console.WriteLine(JsonSerializer.Serialize(output1));
        
        Person p2 = new Person();
        var output2 = new Wrapper<Person>(p2);
        Console.WriteLine(JsonSerializer.Serialize(output2));
        
        Person p3 = null;
        var output3 = new Wrapper<Person>(p3);
        Console.WriteLine(JsonSerializer.Serialize(output3));
    }
}

public class Wrapper<T> where T : class {
    public T optionalOfMyClass { get; set; }
    public Wrapper(T data) {
        optionalOfMyClass = data;
    }
}

public class Person {
    public int Id { get; set; }

    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public string Name { get; set; }
}

在此处找到 dotnet fiddle。