如何使用Json.Net序列化/反序列化带有自定义键的字典?

Question

我有以下类，我将其用作字典中的键:

    public class MyClass
    {
        private readonly string _property;
        public MyClass(string property)
        {
            _property = property;
        }
        public string Property
        {
            get { return _property; }
        }
        public override bool Equals(object obj)
        {
            MyClass other = obj as MyClass;
            if (other == null) return false;
            return _property == other._property;
        }
        public override int GetHashCode()
        {
            return _property.GetHashCode();
        }
    }

我正在运行的测试在这里:

    [Test]
    public void SerializeDictionaryWithCustomKeys()
    {
        IDictionary<MyClass, object> expected = new Dictionary<MyClass, object>();
        expected.Add(new MyClass("sth"), 5.2);
        JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All };
        string output = JsonConvert.SerializeObject(expected, Formatting.Indented, jsonSerializerSettings);
        var actual = JsonConvert.DeserializeObject<IDictionary<MyClass, object>>(output, jsonSerializerSettings);
        CollectionAssert.AreEqual(expected, actual);
    }

测试失败，因为Json。Net似乎在字典键上使用ToString()方法，而不是正确地序列化它们。上面测试的结果json是:

{
  "$type": "System.Collections.Generic.Dictionary`2[[RiskAnalytics.UnitTests.API.TestMarketContainerSerialisation+MyClass, RiskAnalytics.UnitTests],[System.Object, mscorlib]], mscorlib",
  "RiskAnalytics.UnitTests.API.TestMarketContainerSerialisation+MyClass": 5.2
}

显然是错误的。我怎样才能使它工作呢?

Answer 1

这应该能奏效:

序列化:

JsonConvert.SerializeObject(expected.ToArray(), Formatting.Indented, jsonSerializerSettings);

通过调用expected.ToArray()，您序列化了KeyValuePair<MyClass, object>对象的数组，而不是字典。

反序列化:

JsonConvert.DeserializeObject<KeyValuePair<IDataKey, object>[]>(output, jsonSerializerSettings).ToDictionary(kv => kv.Key, kv => kv.Value);

这里你反序列化数组，然后用.ToDictionary(...)调用检索字典。

我不确定输出是否符合您的期望，但肯定它通过了相等断言。

Answer 2

Grx70的答案很好-只是在这里添加了一个替代解决方案。我在一个Web API项目中遇到了这个问题，我没有调用SerializeObject，但允许序列化自动发生。

这个基于Brian Rogers对类似问题的回答的自定义JsonConverter对我来说很有用:

public class DeepDictionaryConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (typeof(IDictionary).IsAssignableFrom(objectType) ||
                TypeImplementsGenericInterface(objectType, typeof(IDictionary<,>)));
    }
    private static bool TypeImplementsGenericInterface(Type concreteType, Type interfaceType)
    {
        return concreteType.GetInterfaces()
               .Any(i => i.IsGenericType && i.GetGenericTypeDefinition() == interfaceType);
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Type type = value.GetType();
        IEnumerable keys = (IEnumerable)type.GetProperty("Keys").GetValue(value, null);
        IEnumerable values = (IEnumerable)type.GetProperty("Values").GetValue(value, null);
        IEnumerator valueEnumerator = values.GetEnumerator();
        writer.WriteStartArray();
        foreach (object key in keys)
        {
            valueEnumerator.MoveNext();
            writer.WriteStartArray();
            serializer.Serialize(writer, key);
            serializer.Serialize(writer, valueEnumerator.Current);
            writer.WriteEndArray();
        }
        writer.WriteEndArray();
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

在我的例子中，我在一个类上序列化Dictionary<MyCustomType, int>属性，其中MyCustomType具有Name和Id的属性。结果如下:

...
"dictionaryProp": [
    [
      {
        "name": "MyCustomTypeInstance1.Name",
        "description": null,
        "id": null
      },
      3
    ],
    [
      {
        "name": "MyCustomTypeInstance2.Name",
        "description": null,
        "id": null
      },
      2
    ]
]
...

Answer 3

更简单，完整的解决方案，使用自定义JsonConverter

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
public class CustomDictionaryConverter<TKey, TValue> : JsonConverter
{
    public override bool CanConvert(Type objectType) => objectType == typeof(Dictionary<TKey, TValue>);
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, ((Dictionary<TKey, TValue>)value).ToList());
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<KeyValuePair<TKey, TValue>[]>(reader).ToDictionary(kv => kv.Key, kv => kv.Value);
}

用法:

[JsonConverter(typeof(CustomDictionaryConverter<KeyType, ValueType>))]
public Dictionary<KeyType, ValueType> MyDictionary;

Answer 4

由于您的类可以轻松地序列化和反序列化为普通字符串，因此可以使用自定义Json转换器完成此操作，同时保持Json的对象结构。

我为此目的编写了一个JsonConverter，以对象样式转换任何字典，而无需使用数组或自定义键类型的类型参数:Json。对象样式

自定义键字典的。NET转换器

要点是手动检查键-值对，并强制对源自Json对象属性的键类型进行序列化。我能给出的最简约的工作示例:

public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
    // Aquire reflection info & get key-value-pairs:
    Type type = value.GetType();
    bool isStringKey = type.GetGenericArguments()[0] == typeof(string);
    IEnumerable keys = (IEnumerable)type.GetProperty("Keys").GetValue(value, null);
    IEnumerable values = (IEnumerable)type.GetProperty("Values").GetValue(value, null);
    IEnumerator valueEnumerator = values.GetEnumerator();
    // Write each key-value-pair:
    StringBuilder sb = new StringBuilder();
    using (StringWriter tempWriter = new StringWriter(sb))
    {
        writer.WriteStartObject();
        foreach (object key in keys)
        {
            valueEnumerator.MoveNext();
            // convert key, force serialization of non-string keys
            string keyStr = null;
            if (isStringKey)
            {
                // Key is not a custom type and can be used directly
                keyStr = (string)key;
            }
            else
            {
                sb.Clear();
                serializer.Serialize(tempWriter, key);
                keyStr = sb.ToString();
                // Serialization can wrap the string with literals
                if (keyStr[0] == '"' && keyStr[str.Length-1] == '"')
                    keyStr = keyStr.Substring(1, keyStr.Length - 1);
                // TO-DO: Validate key resolves to single string, no complex structure
            }
            writer.WritePropertyName(keyStr);
            // default serialize value
            serializer.Serialize(writer, valueEnumerator.Current);
        }
        writer.WriteEndObject();
    }
}

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    // Aquire reflection info & create resulting dictionary:
    Type[] dictionaryTypes = objectType.GetGenericArguments();
    bool isStringKey = dictionaryTypes[0] == typeof(string);
    IDictionary res = Activator.CreateInstance(objectType) as IDictionary;
    // Read each key-value-pair:
    object key = null;
    object value = null;
    while (reader.Read())
    {
        if (reader.TokenType == JsonToken.EndObject)
            break;
        if (reader.TokenType == JsonToken.PropertyName)
        {
            key = isStringKey ? reader.Value : serializer.Deserialize(reader, dictionaryTypes[0]);
        }
        else
        {
            value = serializer.Deserialize(reader, dictionaryTypes[1]);
            res.Add(key, value);
            key = null;
            value = null;
        }
    }
    return res;
}

使用这样的转换器，JSON对象可以直接用作字典，正如您所期望的那样。换句话说，现在可以这样做:

{
  MyDict: {
    "Key1": "Value1",
    "Key2": "Value2"
    [...]
  }
}

而不是:

{
  MyDict: [
    ["Key1", "Value1"],
    ["Key2", "Value2"]
    [...]
  ]
}