在某些条件下进行序列化时忽略属性

问题描述

Json.net具有一个非常有用的属性，可以在名为NullValueHandling的JsonPropertyAttribute上进行设置.如果您装饰这样的属性:

Json.net has a very useful property that can be set on the JsonPropertyAttribute called NullValueHandling. If you decorate a property like this:

[JsonProperty(NullValueHandling=NullValueHandling.Ignore)]
string MyProp { get; set; }

然后，如果MyProp为null，则根本不会将其包含在输出中.

Then if MyProp is null, it won't be included in the output at all.

我想做类似的事情，但排除条件不同.例如-说我们有一个枚举

I would like to do something similar, but with a different condition for exclusion. For example - say we have an enum

public enum MyEnum { None = 0, Value1 = 1, Value2 = 2, Value3 = 4 };

还有财产

MyEnum MyProp { get; set; }

然后，如果MyProp == MyEnum.None，我希望将MyProp从输入中完全排除.

Then I'd like to have MyProp completely excluded from the input if MyProp == MyEnum.None.

我知道一种解决方案是使用MyEnum?而不是MyEnum，然后我可以再次使用NullValueHandling，但是我不能在这里使用nullable.我以为我也许可以使用JsonConverter，所以我尝试对StringEnumConverter进行子类化(因为我希望将它们理想地输出为字符串):

I know one solution would be to use MyEnum? instead of MyEnum and then I could use NullValueHandling again, but I can't use nullable here. I thought I might be able to use a JsonConverter so I tried to subclass StringEnumConverter (because I want them outputted as strings ideally):

    public class MyEnumConverter : Newtonsoft.Json.Converters.StringEnumConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(MyEnum);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            // don't write if value is none
            var v = (MyEnum)value;
            if (v == MyEnum.None)
            {
                // what to do here? The two options below both include the property as null
                //writer.WriteNull();
                //serializer.Serialize(writer, null);
                return;        // just returning without doing anything will break the serialization
            }
            base.WriteJson(writer, value, serializer);
        }
    }

我可以还是应该尝试对JsonProperty进行子类化?如果是这样，我需要重写什么才能得到我想要的行为?

Can I, or should I, try subclassing JsonProperty? And if so, what would I need to override to get the behavior I want?

我希望避免将转换器附加到包含此属性的类上，因为那样的话，我必须手动序列化整个过程，这很痛苦.

I hoping to avoid having to attach a converter to the class that contains this property because then I have to manually serialize the whole thing, which is a pain.

推荐答案

您可以使用签名为public bool ShouldSerialize*PropertyName*()的方法.

You can use a method with the signature public bool ShouldSerialize*PropertyName*().

public enum MyEnum { None = 0, Value1 = 1, Value2 = 2, Value3 = 4 };

public class SomeClass
{
    public MyEnum MyProp { get; set; }
    public string Test = "aaaa";

    public bool ShouldSerializeMyProp()
    {
        return MyProp != MyEnum.None;
    }
}

---

var retVal1 = JsonConvert.SerializeObject(new SomeClass() { MyProp= MyEnum.None });
var retVal2 = JsonConvert.SerializeObject(new SomeClass() { MyProp = MyEnum.Value1 });

输出:

retVal1:{"Test":"aaaa"}

retVal2:{"Test":"aaaa","MyProp":1}

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