Question

我需要将我的类转换为JSON并使用Json.NET。但我可以使用不同的JSON结构，例如：

{
    name: "Name",
    type: "simple1",
    value: 100
};

或

{
    name: "Name",
    type: {
        optional1: {
            setting1: "s1",
            setting2: "s2",
            ///etc.
    },
    value: 100
};

我的C＃代码是：

public class Configuration
{
    [JsonProperty(PropertyName = "name")]
    public string Name{ get; set; }

    [JsonProperty(PropertyName = "type")]
    public MyEnumTypes Type { get; set; }

    public OptionalType TypeAdditionalData { get; set; }

    [JsonProperty(PropertyName = "value")]
    public int Value { get; set; }
    public bool ShouldSerializeType()
    {
        OptionalSettingsAttribute optionalSettingsAttr = this.Type.GetAttributeOfType<OptionalSettingsAttribute>();
        return optionalSettingsAttr == null;
    }

    public bool ShouldSerializeTypeAdditionalData()
    {
        OptionalSettingsAttribute optionalSettingsAttr = this.Type.GetAttributeOfType<OptionalSettingsAttribute>();
        return optionalSettingsAttr != null;
    }
}

public enum MyEnumTypes 
{
    [EnumMember(Value = "simple1")]
    Simple1,

    [EnumMember(Value = "simple2")]
    Simple2,

    [OptionalSettingsAttribute]
    [EnumMember(Value = "optional1")]
    Optional1,

    [EnumMember(Value = "optional2")]
    [OptionalSettingsAttribute]
    Optional2
}

我的想法是Configuration.Type - 值没有属性OptionalSettingsAttribute - 将其序列化为type: "simple1"。否则 - 使用Configuration.Type - 值作为类型的值键（type: { optional1: {} }）和Configuration.TypeAdditionalData中的值optional1 - 值（如上面的2个简单JSON）。

我尝试创建自定义转换器，例如：

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

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return serializer.Deserialize<Configuration>(reader);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        //my changes here

        serializer.Serialize(writer, value);
    }

但是当我向[JsonConverter(typeof(ConfigurationCustomConverter))]类添加Configuration属性时：

[JsonConverter(typeof(ConfigurationCustomConverter))]
public class Configuration

并调用JsonConvert.SerializeObject(configurationObj);我收到了下一个错误：

使用类型＆＃39;配置＆＃39;检测到自引用循环。路径＆＃39;。

您是否有任何想法如何更改我的代码以将我的类序列化为2个不同的JSON结构？ 注意：我不会使用同一个类来反序列化JSON。

谢谢！

Answer 1

您获得Self referencing loop detected异常的原因是转换器的WriteJson方法是递归调用自身的。使用[JsonConverter(typeof(ConfigurationCustomConverter))]将转换器应用于类型时，WriteJson()方法将无条件替换 Json.NET的默认实现。因此，你内心的呼唤：

public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
    //my changes here
    serializer.Serialize(writer, value);
}

会导致堆栈溢出。 Json.NET注意到这一点，而是抛出你看到的异常。有关详细信息，请参阅JSON.Net throws StackOverflowException when using [JsonConvert()]。设置ReferenceLoopHandling.Ignore只会导致跳过无限递归，使对象变空。

您有几个选项可以解决此问题：

您可以手动编写Type和TypeAdditionalData以外的所有属性名称和值，然后最后写出自定义"type"属性。例如：

[JsonConverter(typeof(ConfigurationConverter))]
public class Configuration
{
    [JsonProperty(PropertyName = "name")]
    public string Name { get; set; }

    public MyEnumTypes Type { get; set; }

    public OptionalType TypeAdditionalData { get; set; }

    [JsonProperty(PropertyName = "value")]
    public int Value { get; set; }
}

class ConfigurationConverter : JsonConverter
{
    const string typeName = "type";

    public override bool CanConvert(Type objectType)
    {
        return typeof(Configuration).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var config = (existingValue as Configuration ?? (Configuration)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator());

        // Populate the regular property values.
        var obj = JObject.Load(reader);
        var type = obj.RemoveProperty(typeName);
        using (var subReader = obj.CreateReader())
            serializer.Populate(subReader, config);

        // Populate Type and OptionalType
        if (type is JValue) // Primitive value
        {
            config.Type = type.ToObject<MyEnumTypes>(serializer);
        }
        else
        {
            var dictionary = type.ToObject<Dictionary<MyEnumTypes, OptionalType>>(serializer);
            if (dictionary.Count > 0)
            {
                config.Type = dictionary.Keys.First();
                config.TypeAdditionalData = dictionary.Values.First();
            }
        }

        return config;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var config = (Configuration)value;
        var contract = (JsonObjectContract)serializer.ContractResolver.ResolveContract(config.GetType());
        writer.WriteStartObject();
        foreach (var property in contract.Properties
            .Where(p => p.Writable && (p.ShouldSerialize == null || p.ShouldSerialize(config)) && !p.Ignored))
        {
            if (property.UnderlyingName == "Type" || property.UnderlyingName == "TypeAdditionalData")
                continue;
            var propertyValue = property.ValueProvider.GetValue(config);
            if (propertyValue == null && serializer.NullValueHandling == NullValueHandling.Ignore)
                continue;
            writer.WritePropertyName(property.PropertyName);
            serializer.Serialize(writer, propertyValue);
        }
        writer.WritePropertyName(typeName);
        if (config.Type.GetCustomAttributeOfEnum<OptionalSettingsAttribute>() == null)
        {
            serializer.Serialize(writer, config.Type);
        }
        else
        {
            var dictionary = new Dictionary<MyEnumTypes, OptionalType>
            {
                { config.Type, config.TypeAdditionalData },
            };
            serializer.Serialize(writer, dictionary);
        }
        writer.WriteEndObject();
    }
}

public class OptionalType
{
    public string setting1 { get; set; }
}

public class OptionalSettingsAttribute : System.Attribute
{
    public OptionalSettingsAttribute()
    {
    }
}

[JsonConverter(typeof(StringEnumConverter))]
public enum MyEnumTypes
{
    [EnumMember(Value = "simple1")]
    Simple1,

    [EnumMember(Value = "simple2")]
    Simple2,

    [OptionalSettingsAttribute]
    [EnumMember(Value = "optional1")]
    Optional1,

    [EnumMember(Value = "optional2")]
    [OptionalSettingsAttribute]
    Optional2
}

public static class EnumExtensions
{
    public static TAttribute GetCustomAttributeOfEnum<TAttribute>(this Enum value)
        where TAttribute : System.Attribute
    {
        var type = value.GetType();
        var memInfo = type.GetMember(value.ToString());
        return memInfo[0].GetCustomAttribute<TAttribute>();
    }
}

public static class JsonExtensions
{
    public static JToken RemoveProperty(this JObject obj, string name)
    {
        if (obj == null)
            return null;
        var property = obj.Property(name);
        if (property == null)
            return null;
        var value = property.Value;
        property.Remove();
        property.Value = null;
        return value;
    }
}

注意我在您的枚举中添加了[JsonConverter(typeof(StringEnumConverter))]。这样可以确保类型始终写为字符串。

示例fiddle。

您可以通过JSON.Net throws StackOverflowException when using [JsonConvert()]中显示的技术禁用对转换器的递归调用，生成默认序列化，根据需要进行修改，然后将其写出来。

您可以通过将Type和TypeAdditionalData标记为[JsonIgnore]并引入其他私有属性来序列化和反序列化"type"来完全避免使用转换器：

public class Configuration
{
    [JsonProperty(PropertyName = "name")]
    public string Name { get; set; }

    [JsonIgnore]
    public MyEnumTypes Type { get; set; }

    [JsonIgnore]
    public OptionalType TypeAdditionalData { get; set; }

    [JsonProperty("type")]
    JToken SerializedType
    {
        get
        {
            if (Type.GetCustomAttributeOfEnum<OptionalSettingsAttribute>() == null)
            {
                return JToken.FromObject(Type);
            }
            else
            {
                var dictionary = new Dictionary<MyEnumTypes, OptionalType>
                {
                    { Type, TypeAdditionalData },
                };
                return JToken.FromObject(dictionary);
            }
        }
        set
        {
            if (value == null || value.Type == JTokenType.Null)
            {
                TypeAdditionalData = null;
                Type = default(MyEnumTypes);
            }
            else if (value is JValue)
            {
                Type = value.ToObject<MyEnumTypes>();
            }
            else
            {
                var dictionary = value.ToObject<Dictionary<MyEnumTypes, OptionalType>>();
                if (dictionary.Count > 0)
                {
                    Type = dictionary.Keys.First();
                    TypeAdditionalData = dictionary.Values.First();
                }
            }
        }
    }

    [JsonProperty(PropertyName = "value")]
    public int Value { get; set; }
}

Answer 2

如果您需要移除该错误，可以配置序列化以忽略参考循环。这是通过使用其中一个SerializaObject()重载来完成的。

JsonConvert.SerializeObject(configurationObj,
                    new JsonSerializerSettings()
                    { 
                        ReferenceLoopHandling = ReferenceLoopHandling.Ignore
                    });

Json.NET不同的json结构，基于枚举值

2 个答案: