Json.net 反序列化 null guid 案例

创建一个 JsonConverter 将 null Json 令牌转换为默认 Guid 值:

Create a JsonConverter that converts a null Json token to a default Guid value:

public class NullToDefaultConverter<T> : JsonConverter where T : struct
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(T);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var token = JToken.Load(reader);
        if (token == null || token.Type == JTokenType.Null)
            return default(T);
        return token.ToObject(objectType); // Deserialize using default serializer
    }

    // Return false instead if you don't want default values to be written as null
    public override bool CanWrite { get { return true; } }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (EqualityComparer<T>.Default.Equals((T)value, default(T)))
            writer.WriteNull();
        else
            writer.WriteValue(value);
    }
}

然后将其应用于您的类型，如下所示:

Then apply it to your type as follows:

public class MyClass
{
    [JsonConverter(typeof(NullToDefaultConverter<Guid>))]
    public Guid Property { get; set; }
}

或者，您可以通过将转换器添加到 T 类型的所有值.htm" rel="noreferrer">JsonSerializerSettings.Converters.而且，要在全球范围内注册这样的转换器，请参阅例如如何在 MVC 4 Web API 中为 Json.NET 设置自定义 JsonSerializerSettings? 用于 Web API，设置 JsonConvert.DefaultSettings asp net core 2.0 无法正常工作 用于 ASP.NET Core 或 在 Json.Net 中全局注册自定义 JsonConverter对于控制台应用程序.

Alternatively, you can apply the converter to all values of type T by adding the converter to JsonSerializerSettings.Converters. And, to register such a converter globally, see e.g.How to set custom JsonSerializerSettings for Json.NET in MVC 4 Web API? for Web API, Setting JsonConvert.DefaultSettings asp net core 2.0 not working as expected for ASP.NET Core or Registering a custom JsonConverter globally in Json.Net for a console app.

如果您为控制台应用程序全局注册转换器，您可能需要禁用它以进行递归调用，如 JSON.Net 在使用 [JsonConvert()] 时抛出 StackOverflowException.

If you do register the converter globally for a console app, you may need to disable it for recursive calls as shown in JSON.Net throws StackOverflowException when using [JsonConvert()].

如果您只需要 反序列化 Guid 的 null 值而不是重新序列化它，则可以应用 [JsonProperty(NullValueHandling = NullValueHandling.Ignore)] 到 Guid 属性, 和 null 值将被忽略，尽管 Guid 值无效:

If you only need to deserialize a null value for a Guid and not re-serialize it as such, you can apply [JsonProperty(NullValueHandling = NullValueHandling.Ignore)] to the Guid property, and null values will ignored despite being invalid Guid values:

public class MyClass
{
    [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
    public Guid Property { get; set; }
}

当然，如果您这样做，您的 Guid 将被重新序列化为 00000000-0000-0000-0000-000000000000".为了改善这种情况，您可以应用 DefaultValueHandling = DefaultValueHandling.Ignore 这将导致在序列化期间省略空的 Guid 值:

Of course if you do this your Guid will be re-serialized as "00000000-0000-0000-0000-000000000000". To ameliorate that you could apply DefaultValueHandling = DefaultValueHandling.Ignore which will cause empty Guid values to be omitted during serialization:

[JsonProperty(NullValueHandling = NullValueHandling.Ignore, DefaultValueHandling = DefaultValueHandling.Ignore)]
public Guid Property { get; set; }

请注意，如果在反序列化期间调用的 参数化构造函数具有非-nullable Guid 参数具有相同的名称，可能需要不同的方法.

Note that if a parameterized constructor called during deserialization has a non-nullable Guid argument with the same name, a different approach may be required.

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