C# Newtonsoft.Json 自定义解串器

Question

我正在使用一个 API 以不同于我过去处理的方式向我返回结果，而且看起来不标准。

例如，这里有一段客户数据：

{
    "CustomerID": {
        "value": "EXAMPLE"
    },
    "CustomerCurrencyID": {
        "value": "USD"
    }
}

那个“值”属性似乎非常不必要，所以我想看看我是否可以一起绕过它并将 JSON 反序列化为一个对象，如下所示：

class Customer {
    public string CustomerID { get; set; }
    public string CustomerCurrencyID { get; set; }
}

我目前正在编写一个自定义的 JsonConverter 来处理这个问题，所以如果我正朝着正确的方向前进，请告诉我，但是任何 tips/tricks 这里将不胜感激！

Answer 1

您可以使用如下通用 custom JsonConverter 执行此操作：

public class WrapWithValueConverter<TValue> : JsonConverter
{
    // Here we take advantage of the fact that a converter applied to a property has highest precedence to avoid an infinite recursion.
    class DTO { [JsonConverter(typeof(NoConverter))] public TValue value { get; set; } public object GetValue() => value; }

    public override bool CanConvert(Type objectType) => typeof(TValue).IsAssignableFrom(objectType);
    
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, new DTO { value = (TValue)value });

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<DTO>(reader)?.GetValue();
}

public class NoConverter : JsonConverter
{
    // NoConverter taken from this answer 
    // By https://whosebug.com/users/3744182/dbc
    // To 
    public override bool CanConvert(Type objectType)  { throw new NotImplementedException(); /* This converter should only be applied via attributes */ }
    public override bool CanRead => false;
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) => throw new NotImplementedException();
    public override bool CanWrite => false;
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
}

然后您可以将其应用到您的模型中，如下所示：

class Customer {
    [JsonConverter(typeof(WrapWithValueConverter<string>))]
    public string CustomerID { get; set; }
    [JsonConverter(typeof(WrapWithValueConverter<string>))]
    public string CustomerCurrencyID { get; set; }
}

演示 fiddle #1 here.

或者，如果你想所有字符串包装在一个{"value": <string value>}对象中，你可以在序列化和反序列化时将转换器添加到JsonSerializerSettings.Converters：

var settings = new JsonSerializerSettings
{
    Converters = { new WrapWithValueConverter<string>() },
};

var model = JsonConvert.DeserializeObject<Customer>(json, settings);

var json2 = JsonConvert.SerializeObject(model, Formatting.Indented, settings);

演示 fiddle #2 here.

如果您的值是 enum 并且您想将其序列化为字符串，您可以使用以下命令将 NoConverter 替换为 StringEnumConverter：

public class WrapEnumWithValueConverter<TEnum> : JsonConverter where TEnum: Enum
{
    // Here we take advantage of the fact that a converter applied to a property has highest precedence to avoid an infinite recursion.
    class DTO { [JsonConverter(typeof(StringEnumConverter))] public TEnum value { get; set; } public object GetValue() => value; }

    public override bool CanConvert(Type objectType) => typeof(TEnum).IsAssignableFrom(objectType);

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, new DTO { value = (TEnum)value });

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<DTO>(reader)?.GetValue();
}

演示 fiddle #3 here.

C# Newtonsoft.Json 自定义解串器

C# Newtonsoft.Json Custom Deserializer

c#

json

json.net