如何以与使用 Json.NET 的对象相同的方式序列化 JObject？

Question

如何控制 JObject 到字符串的序列化？

我有一些返回 JObject 的 API，我通常会应用一些更改并保留或返回它们。我想避免保留空属性并应用一些额外的格式，但 JsonConvert 似乎完全忽略了我的设置。

这是问题的示例：

// startup.cs has the following
services.AddMvc().AddJsonOptions(o =>
{
    o.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
});

public class SampleController : Controller
{
    JsonSerializerSettings _settings = new JsonSerializerSettings
    {
        NullValueHandling = NullValueHandling.Ignore
    };

    [HttpPost]
    [Route("object")]
    public object PostObject([FromBody] SomeObject data)
    {
        return JsonConvert.SerializeObject(data, _settings);
    }

    [HttpPost]
    [Route("jobject")]
    public object PostJObject([FromBody] JObject data)
    {
        return JsonConvert.SerializeObject(data, _settings);
    }

    public class SomeObject
    {
        public string Foo { get; set; }
        public string Bar { get; set; }
    }
}

发帖{ "Foo": "Foo", "Bar": null }:

• /object 返回{"Foo":"Foo"}
• /jobject 返回{"Foo":"Foo","Bar":null}

我希望 JObject 方法返回与使用对象相同的输出 json。我如何在不创建助手的情况下实现这一目标？有没有办法使用相同的设置序列化 JObject？

Answer 1

与 NewtonSoft 框架完美集成的解决方案是提供一个自定义 JObject 转换器，该转换器支持 NamingStrategy。

JObject 自定义转换器

public class JObjectNamingStrategyConverter : JsonConverter<JObject> {

private NamingStrategy NamingStrategy { get; }

public JObjectNamingStrategyConverter (NamingStrategy strategy) {
    if (strategy == null) {
        throw new ArgumentNullException (nameof (strategy));
    }
    NamingStrategy = strategy;
}

public override void WriteJson (JsonWriter writer, JObject value, JsonSerializer serializer) {
    writer.WriteStartObject ();
    foreach (JProperty property in value.Properties ()) {
        var name = NamingStrategy.GetPropertyName (property.Name, false);
        writer.WritePropertyName (name);
        serializer.Serialize (writer, property.Value);
    }
    writer.WriteEndObject ();
}

public override JObject ReadJson (JsonReader reader, Type objectType, JObject existingValue, bool hasExistingValue, JsonSerializer serializer) {
    throw new NotImplementedException ();
}
}

用法

var snakeNameStrategy = new SnakeCaseNamingStrategy ();
var jsonSnakeSettings = new JsonSerializerSettings {
Formatting = Formatting.Indented,
Converters = new [] { new JObjectNamingStrategyConverter (snakeNameStrategy) },
   ContractResolver = new DefaultContractResolver {
       NamingStrategy = snakeNameStrategy
   },
};

var json = JsonConvert.SerializeObject (obj, jsonSnakeSettings);

您可以在 GitHub 上找到有效的 PoC。

Answer 2

我能够做到这一点的唯一方法是首先将JObject转换为string，然后将该字符串反序列化为ExpandoObject（不要反序列化为object，因为你会回来的JObject)。 ExpandoObject 就像一个字典，这将导致JsonConvert 实际调用配置的名称大小写策略。我不确定为什么 Newtonsoft.Json 的作者没有像处理字典类型那样处理 JObject 类型，但至少这种解决方法有效。

例子：

// Construct a JObject.
var jObject = JObject.Parse("{ SomeName: \"Some value\" }");

// Deserialize the object into an ExpandoObject (don't use object, because you will get a JObject).
var payload = JsonConvert.DeserializeObject<ExpandoObject>(jObject.ToString());

// Now you can serialize the object using any serializer settings you like.
var json = JsonConvert.SerializeObject(payload, new JsonSerializerSettings
{
    ContractResolver = new DefaultContractResolver
    {
        NamingStrategy = new CamelCaseNamingStrategy
        {
            // Important! Make sure to set this to true, since an ExpandoObject is like a dictionary.
            ProcessDictionaryKeys = true,
        }
    }
}
);

Console.WriteLine(json); // Outputs: {"someName":"Some value"}

我在这里用ExpandoObject 找到了诀窍：JObject & CamelCase conversion with JSON.Net

Answer 3

当JObject 被序列化时，它的原始 JSON 被写入。 JsonSerializerSettings 不会影响其写入的 JSON。