NewtonSoft Json DeserializeObject 空 Guid 字段

Question

我正在使用带有 HTML CSS jQuery KnockoutJs 前端的 ASP.NET MVC C#。

我的 HTML 页面上有一个模式联系表。这个想法是，如果我创建一个新联系人，模态表单会弹出一个空白值，包括一个空白的隐藏 id 字段。

如果我编辑联系人，则会弹出模式表单，其中包含已填写的字段，包括隐藏的 id 字段。

在我的控制器中，我打算这样做：

public JsonResult Contact(string values)
{
    var contact = JsonConvert.DeserializeObject<contact>(values);

    if (contact.Id.Equals(Guid.Empty))
    {
         // create a new contact in the database
    } else
    {
        // update an existing one
    }
}

但是，我收到一条错误消息，提示 can't convert "" to type Guid

你如何使用 NewtonSoft Json 解决这个问题，我在 Custom JsonConverter 上查看了here，它似乎是正确的，但我不知道该去哪里有了这个。

Answer 1

自定义转换器看起来像这样，但我觉得对于如此微不足道的事情来说它有点矫枉过正。

/// <summary>
/// Converts a <see cref="Guid"/> to and from its <see cref="System.String"/> representation.
/// </summary>
public class GuidConverter : JsonConverter
{
    /// <summary>
    /// Determines whether this instance can convert the specified object type.
    /// </summary>
    /// <param name="objectType">Type of the object.</param>
    /// <returns>Returns <c>true</c> if this instance can convert the specified object type; otherwise <c>false</c>.</returns>
    public override bool CanConvert(Type objectType)
    {
        return objectType.IsAssignableFrom(typeof(Guid));
    }

    /// <summary>
    /// Reads the JSON representation of the object.
    /// </summary>
    /// <param name="reader">The <see cref="JsonReader"/> to read from.</param>
    /// <param name="objectType">Type of the object.</param>
    /// <param name="existingValue">The existing value of object being read.</param>
    /// <param name="serializer">The calling serializer.</param>
    /// <returns>The object value.</returns>
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        try
        {
            return serializer.Deserialize<Guid>(reader);
        }
        catch
        {
            return Guid.Empty;
        }
    }

    /// <summary>
    /// Writes the JSON representation of the object.
    /// </summary>
    /// <param name="writer">The <see cref="JsonWriter"/> to write to.</param>
    /// <param name="value">The value.</param>
    /// <param name="serializer">The calling serializer.</param>
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        serializer.Serialize(writer, value);
    }
}

用法：

class Contact
{
    [JsonConverter(typeof(GuidConverter))]
    public Guid Id { get; set; }
}

或者：

var contact = JsonConvert.DeserializeObject<contact>(values, new GuidConverter());

编辑

我认为你的 JSON 看起来很像这样：

{
    "id": "",
    "etc": "..."
}

如果您可以这样做，问题可能会得到解决：

{
    "id": null,
    "etc": "..."
}

Answer 2

我遇到了 Guid.Empty (00000000-0000-0000-0000-000000000000) 值被反序列化为 Null 指南导致错误的问题。当我将 JsonSerializerSettings.DefaultValueHandling 值设置为 DefaultValueHandling.IgnoreAndPopulate 时，反序列化 Guid 属性被设置为默认值

var serializedObject = JsonConvert.DeserializeObject<T>(serializedString, new JsonSerializerSettings { DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate });

Answer 3

GUID 和 JSON 字符串的完整示例

string content = "{\"data\":{\"Type\":\"Foo\",\"Description\":\"bar \",\"Software\":\"baz\",\"Version\":\"qux\",\"Url\":\"http://example.com\",\"DatabasePortNumber\":1,\"Id\":\"2cdc66f1-0000-0000-39ac-233c00000000\"}}";

var result_SystemText = System.Text.Json.JsonSerializer.Deserialize<SystemApplicationResponse>(content);  //Will result in null-object
var result_Newtonsoft = Newtonsoft.Json.JsonConvert.DeserializeObject<SystemApplicationResponse>(content); //Will result in correctly serialized object

    public class SystemApplicationResponse
    {
        public SystemApplicationDto Data { get; set; }
    }


    public class SystemApplicationDto
    {
        public SystemApplicationDtoType Type { get; set; }

        public string Description { get; set; }

        public string Software { get; set; }

        public string Version { get; set; }
        public string Url { get; set; }

        public int DatabasePortNumber { get; set; }
        public System.Guid Id { get; set; }
    }

    public enum SystemApplicationDtoType
    {
        Foo = 0
    }

参考：https://github.com/dotnet/runtime/issues/31465#