Newtonsoft Json 将字典反序列化为来自 DataContractJsonSerializer 的键/值列表

问题描述

我有一个使用 DataContractJsonSerializer 序列化到存储的字典，我想使用 Newtonsoft.Json 对其进行反序列化.

I have a dictionary serialized to storage with DataContractJsonSerializer which I would like to deserialize with Newtonsoft.Json.

DataContractJsonSerializer 已将 Dictionary 序列化为键/值对列表:

The DataContractJsonSerializer has serialized the Dictionary to a list of Key/Value pairs:

{"Dict":[{"Key":"Key1","Value":"Val1"},{"Key":"Key2","Value":"Val2"}]}

我可以为 JsonConvert.DeserializeObject<>() 提供什么很酷的选项，使其支持该数据格式和来自 Newtonsoft.Json 的格式?

Is there any cool options I can give the JsonConvert.DeserializeObject<>() that will make it support both that data format and the format from Newtonsoft.Json?

{"Dict":{"Key1":"Val1","Key2":"Val2"}}

是 Newtonsoft.Json 创建的漂亮格式，我希望在过渡期间能够同时读取旧的 DataContract 格式和新的 Newtonsoft 格式.

Is the pretty format Newtonsoft.Json creates, and I would like to be able to read both the old DataContract format and the new Newtonsoft format in a transition period.

简化示例:

    //[JsonArray]
    public sealed class Data
    {
        public IDictionary<string, string> Dict { get; set; }
    }

    [TestMethod]
    public void TestSerializeDataContractDeserializeNewtonsoftDictionary()
    {
        var d = new Data
        {
            Dict = new Dictionary<string, string>
            {
                {"Key1", "Val1"},
                {"Key2", "Val2"},
            }
        };

        var oldJson = String.Empty;
        var formatter = new DataContractJsonSerializer(typeof (Data));
        using (var stream = new MemoryStream())
        {
            formatter.WriteObject(stream, d);
            oldJson = Encoding.UTF8.GetString(stream.ToArray());
        }

        var newJson = JsonConvert.SerializeObject(d);
        // [JsonArray] on Data class gives:
        //
        // System.InvalidCastException: Unable to cast object of type 'Data' to type 'System.Collections.IEnumerable'.

        Console.WriteLine(oldJson);
        // This is tha data I have in storage and want to deserialize with Newtonsoft.Json, an array of key/value pairs
        // {"Dict":[{"Key":"Key1","Value":"Val1"},{"Key":"Key2","Value":"Val2"}]}

        Console.WriteLine(newJson);
        // This is what Newtonsoft.Json generates and should also be supported:
        // {"Dict":{"Key1":"Val1","Key2":"Val2"}}

        var d2 = JsonConvert.DeserializeObject<Data>(newJson);
        Assert.AreEqual("Val1", d2.Dict["Key1"]);
        Assert.AreEqual("Val2", d2.Dict["Key2"]);

        var d3 = JsonConvert.DeserializeObject<Data>(oldJson);
        // Newtonsoft.Json.JsonSerializationException: Cannot deserialize the current JSON array (e.g. [1,2,3]) into 
        // type 'System.Collections.Generic.IDictionary`2[System.String,System.String]' because the type requires a JSON 
        // object (e.g. {"name":"value"}) to deserialize correctly.
        //
        // To fix this error either change the JSON to a JSON object (e.g. {"name":"value"}) or change the deserialized type
        // to an array or a type that implements a collection interface (e.g. ICollection, IList) like List<T> that can be 
        // deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from
        // a JSON array.
        //
        // Path 'Dict', line 1, position 9.

        Assert.AreEqual("Val1", d3.Dict["Key1"]);
        Assert.AreEqual("Val2", d3.Dict["Key2"]);
    }

推荐答案

您可以为此使用自定义转换器，具体取决于字典以什么标记开头，将其反序列化为 JSON.NET 的默认方式，或将其反序列化为数组并然后将该数组转换为 Dictionary:

You could use a custom converter for this, depending on what token the dictionary starts with, deserialize it JSON.NET's default way, or deserialize it into an array and then turn that array into a Dictionary:

public class DictionaryConverter : JsonConverter
{
    public override object ReadJson(
        JsonReader reader,
        Type objectType,
        object existingValue,
        JsonSerializer serializer)
    {
        IDictionary<string, string> result;

        if (reader.TokenType == JsonToken.StartArray)
        {
            JArray legacyArray = (JArray)JArray.ReadFrom(reader);

            result = legacyArray.ToDictionary(
                el => el["Key"].ToString(),
                el => el["Value"].ToString());
        }
        else 
        {
            result = 
                (IDictionary<string, string>)
                    serializer.Deserialize(reader, typeof(IDictionary<string, string>));
        }

        return result;
    }

    public override void WriteJson(
        JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override bool CanConvert(Type objectType)
    {
        return typeof(IDictionary<string, string>).IsAssignableFrom(objectType);
    }

    public override bool CanWrite 
    { 
        get { return false; } 
    }
}

然后，您可以使用 JsonConverter 属性来装饰 Data 类中的 Dict 属性:

Then, you can decorate the Dict property in the Data class with a JsonConverter attribute:

public sealed class Data
{
    [JsonConverter(typeof(DictionaryConverter))]
    public IDictionary<string, string> Dict { get; set; }
}

然后反序列化两个字符串应该按预期工作.

Then deserializing both strings should work as expected.

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