c# - 在过滤掉某些属性的同时序列化 JSON.NET JObject

Question

我的代码中有一个大型任意 JSON 结构作为 JObject 引用。

我想序列化这个结构，除非我遇到一个 JObject 包含一个名为 type 且值为 "encrypted" 的属性，那么我想要在写入对象之前删除相邻的 data 属性。

换句话说，如果我遇到这种情况:

{
  type: "encrypted",
  name: "some-name",
  data: "<base64-string>"
}

它将被序列化为:

{
  type: "encrypted",
  name: "some-name"
}

我不能改变结构，在改变之前克隆它效率太低，所以我尝试使用 JsonConverter 如下:

public class RemoveEncryptedDataSerializer : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(JObject);
    }

    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)
    {
        var o = (JObject)value;
        if (o.Value<string>("type") != "encrypted")
        {
            o.WriteTo(writer);
            return;
        }

        var copy = o.DeepClone();
        copy["data"]?.Parent.Remove();
        copy.WriteTo(writer);
    }
}

然而，CanConvert 函数似乎只用不是从 JToken 派生的类型调用，所以我的 WriteJson 函数从未被调用。

还有其他方法可以实现吗？

---

编辑:下面是一些您可以用于测试的代码:

[TestMethod]
public void ItShouldExcludeEncryptedData()
{
    var input = JObject.Parse(@"
    {
        a: {
            type: 'encrypted',
            name: 'some-name',
            data: 'some-data'
        }
    }");

    var expected = JObject.Parse(@"
    {
        a: {
            type: 'encrypted',
            name: 'some-name',
        }
    }");

    var output = input.ToString(Formatting.Indented, new RemoveEncryptedDataSerializer());

    Assert.AreEqual(
        expected.ToString(Formatting.Indented),
        output);
}

Answer 1

需要构建转换器来处理 JToken，并且它必须递归工作以确保所有加密数据都被编辑。

我能够让以下转换器工作:

public class RemoveEncryptedDataConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return typeof(JToken).IsAssignableFrom(objectType);
    }

    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)
    {
        JToken token = (JToken)value;
        if (token.Type == JTokenType.Object)
        {
            bool omitDataProperty = token.Value<string>("type") == "encrypted";

            writer.WriteStartObject();
            foreach (var prop in token.Children<JProperty>())
            {
                if (omitDataProperty && prop.Name == "data")
                    continue;

                writer.WritePropertyName(prop.Name);
                serializer.Serialize(writer, prop.Value);  // recurse
            }
            writer.WriteEndObject();
        }
        else if (token.Type == JTokenType.Array)
        {
            writer.WriteStartArray();
            foreach (var item in token.Children())
            {
                serializer.Serialize(writer, item);  // recurse
            }
            writer.WriteEndArray();
        }
        else // JValue
        {
            token.WriteTo(writer);
        }
    }
}

工作演示:https://dotnetfiddle.net/0K61Bz

---

如果您想直接通过流使用 JsonWriter，您可以将转换器中的逻辑重构为递归扩展方法并使用它。如果您不使用序列化程序，则不需要转换器。

public static class JsonExtensions
{
    public static void RedactedWriteTo(this JToken token, JsonWriter writer)
    {
        if (token.Type == JTokenType.Object)
        {
            bool omitDataProperty = token.Value<string>("type") == "encrypted";

            writer.WriteStartObject();
            foreach (var prop in token.Children<JProperty>())
            {
                if (omitDataProperty && prop.Name == "data")
                    continue;

                writer.WritePropertyName(prop.Name);
                prop.Value.RedactedWriteTo(writer);  // recurse
            }
            writer.WriteEndObject();
        }
        else if (token.Type == JTokenType.Array)
        {
            writer.WriteStartArray();
            foreach (var item in token.Children())
            {
                item.RedactedWriteTo(writer);  // recurse
            }
            writer.WriteEndArray();
        }
        else // JValue
        {
            token.WriteTo(writer);
        }
    }
}

然后你可以像这样使用它，其中 stream 是你的输出流，input 是你的 JObject:

using (StreamWriter sw = new StreamWriter(stream))  // or StringWriter if you prefer
using (JsonWriter writer = new JsonTextWriter(sw))
{
    writer.Formatting = Formatting.Indented;
    input.RedactedWriteTo(writer);
}

fiddle :https://dotnetfiddle.net/l949HU