反序列化派生类时如何忽略基类JsonConverter? [英] How to ignore base class JsonConverter when deserializing derived classes?

问题描述

我有一个抽象基类:

[JsonConverter(typeof(Converter))]
public abstract class TextComponent {
    ...
    public bool Bold { get; set; }
    public TextComponent[] Extra { get; set; }
    ...
}

还有更多继承自它的类.这些类之一是StringComponent:

And more classes which inherits from it. One of those classes is StringComponent:

public sealed class StringComponent : TextComponent
{
    public string Text { get; set; }

    public StringComponent(string text)
    {
        Text = text;
    }
}

Converter，它是应用于TextComponent的JsonConverter，看起来像这样:

Converter, which is a JsonConverter applied to TextComponent looks like this:

private sealed class Converter : JsonConverter
{
    ....

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue,
        JsonSerializer serializer)
    {
        var tok = JToken.Load(reader);
        switch (tok)
        {
            ...
            case JObject x:
                var dic = (IDictionary<string, JToken>) x;
                if (dic.ContainsKey("text")) return x.ToObject<StringComponent>();
                ...
            ...
        }
    }
    ...
    public override bool CanConvert(Type objectType) => objectType == typeof(TextComponent);
}

问题:

var str = "{\"text\":\"hello world\"}";
var obj = JsonConvert.DeserializeObject<TextComponent>(str);
// this doesn't work either:
var obj = JsonConvert.DeserializeObject<StringComponent>(str);

这进入一个无限的循环"，最终导致一个StackOverflow，因为在调用DeserializeObject<Stringcomponent>或ToObject<StringComponent>时，使用了基类的JsonConverter(Converter)，它再次调用了这些方法.这不是所需的行为.序列化派生类时，它们不应使用基类的JsonConverter.如果您查看Converter的CanConvert方法，我也只允许将它用于TextComponent，而不允许其用于任何派生类.

This goes into an infinite "loop" eventually resulting in a StackOverflow, because when calling DeserializeObject<Stringcomponent> or ToObject<StringComponent>, the JsonConverter of the base class (the Converter) is used which again calls those methods. This is not the desired behavior. When serializing derived classes, they should not be using base class's JsonConverter. If you look at CanConvert method of the Converter, I'm also only allowing it for TextComponent only, not for any of it's derived classes.

那我该如何解决呢?

推荐答案

您是否尝试从基类中删除[JsonConvert]属性?在我的示例中，我手动调用了自定义"转换器:

Did you try to remove the [JsonConvert]-attribute from your base class? In my example I invoke my "custom" converter manually: https://github.com/Code-Inside/Samples/blob/b635580a4966b1b77c93a8b682389c6cf06d2da6/2015/JsonConvertIssuesWithBaseClasses/JsonConvertIssuesWithBaseClasses/Program.cs#L36-L79

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