c# - 子属性的 JSON .NET 自定义名称解析器

Question

我有一个从 MongoDB 返回 JSON 对象的 API，其中一个属性是“开放式”文档，这意味着它可以是该属性的任何有效 JSON。我不知道属性的名称是什么，它们可以是任何字符串。我只知道这个特定的属性需要序列化完全它在数据库中的存储方式。因此，如果最初存储的属性名称是“Someproperty”，则 JSON 中的序列化响应需要是“Someproperty”，而不是“someProperty”。

我们有这样的配置:

ContractResolver = new CamelCasePropertyNamesContractResolver();

在我们的 CustomJsonSerializer 中，但它在返回“开放式”JSON 时弄乱了响应的格式。当实际上我们希望响应与它们在 MongoDB (BSON) 中的存储方式完全相同时，所有这些属性都是驼峰式的。我知道在通过数据库存储/检索时，值会保持大小写，所以这不是问题。

我如何告诉 JSON.net 基本上绕过特定数据点的所有子属性的 CamelCasePropertyNameResolver？

编辑:只是为了提供更多信息，并分享我已经尝试过的内容:

我想像这样覆盖 PropertyNameResolver:

protected override string ResolvePropertyName(string propertyName)
{
      if (propertyName.ToLower().Equals("somedocument"))
      {
                return propertyName;
      }
      else return base.ResolvePropertyName(propertyName);
}

但是，如果我有这样的 JSON 结构:

{
   "Name" : "MyObject",
   "DateCreated" : "11/14/2016",
   "SomeDocument" : 
   {
      "MyFirstProperty" : "foo",
      "mysecondPROPERTY" : "bar",
      "another_random_subdoc" : 
      {
         "evenmoredata" : "morestuff"
      }
   }
}

然后我需要所有属性、任何子属性的名称都保持原样。我发布的上述覆盖(我相信)只会忽略与“somedocument”的完全匹配，并且仍然会驼峰式排列所有子属性。

Answer 1

你可以做的是，对于有问题的属性，创建一个 custom JsonConverter，它使用由不同的契约(Contract)解析器创建的不同的 JsonSerializer 序列化有问题的属性值，如下所示:

public class AlternateContractResolverConverter : JsonConverter
{
    [ThreadStatic]
    static Stack<Type> contractResolverTypeStack;

    static Stack<Type> ContractResolverTypeStack { get { return contractResolverTypeStack = (contractResolverTypeStack ?? new Stack<Type>()); } }

    readonly IContractResolver resolver;

    JsonSerializerSettings ExtractAndOverrideSettings(JsonSerializer serializer)
    {
        var settings = serializer.ExtractSettings();
        settings.ContractResolver = resolver;
        settings.CheckAdditionalContent = false;
        if (settings.PreserveReferencesHandling != PreserveReferencesHandling.None)
        {
            // Log an error throw an exception?
            Debug.WriteLine(string.Format("PreserveReferencesHandling.{0} not supported", serializer.PreserveReferencesHandling));
        }
        return settings;
    }

    public AlternateContractResolverConverter(Type resolverType)
    {
        if (resolverType == null)
            throw new ArgumentNullException("resolverType");
        resolver = (IContractResolver)Activator.CreateInstance(resolverType);
        if (resolver == null)
            throw new ArgumentNullException(string.Format("Resolver type {0} not found", resolverType));
    }

    public override bool CanRead { get { return ContractResolverTypeStack.Count == 0 || ContractResolverTypeStack.Peek() != resolver.GetType(); } }
    public override bool CanWrite { get { return ContractResolverTypeStack.Count == 0 || ContractResolverTypeStack.Peek() != resolver.GetType(); } }

    public override bool CanConvert(Type objectType)
    {
        throw new NotImplementedException("This contract resolver is intended to be applied directly with [JsonConverter(typeof(AlternateContractResolverConverter), typeof(SomeContractResolver))] or [JsonProperty(ItemConverterType = typeof(AlternateContractResolverConverter), ItemConverterParameters = ...)]");
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        using (ContractResolverTypeStack.PushUsing(resolver.GetType()))
            return JsonSerializer.CreateDefault(ExtractAndOverrideSettings(serializer)).Deserialize(reader, objectType);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        using (ContractResolverTypeStack.PushUsing(resolver.GetType()))
            JsonSerializer.CreateDefault(ExtractAndOverrideSettings(serializer)).Serialize(writer, value);
    }
}

internal static class JsonSerializerExtensions
{
    public static JsonSerializerSettings ExtractSettings(this JsonSerializer serializer)
    {
        // There is no built-in API to extract the settings from a JsonSerializer back into JsonSerializerSettings,
        // so we have to fake it here.
        if (serializer == null)
            throw new ArgumentNullException("serializer");
        var settings = new JsonSerializerSettings
        {
            CheckAdditionalContent = serializer.CheckAdditionalContent,
            ConstructorHandling = serializer.ConstructorHandling,
            ContractResolver = serializer.ContractResolver,
            Converters = serializer.Converters,
            Context = serializer.Context,
            Culture = serializer.Culture,
            DateFormatHandling = serializer.DateFormatHandling,
            DateFormatString = serializer.DateFormatString,
            DateParseHandling = serializer.DateParseHandling,
            DateTimeZoneHandling = serializer.DateTimeZoneHandling,
            DefaultValueHandling = serializer.DefaultValueHandling,
            EqualityComparer = serializer.EqualityComparer,
            // No Get access to the error event, so it cannot be copied.
            // Error = += serializer.Error
            FloatFormatHandling = serializer.FloatFormatHandling,
            FloatParseHandling = serializer.FloatParseHandling,
            Formatting = serializer.Formatting,
            MaxDepth = serializer.MaxDepth,
            MetadataPropertyHandling = serializer.MetadataPropertyHandling,
            MissingMemberHandling = serializer.MissingMemberHandling,
            NullValueHandling = serializer.NullValueHandling,
            ObjectCreationHandling = serializer.ObjectCreationHandling,
            ReferenceLoopHandling = serializer.ReferenceLoopHandling,
            // Copying the reference resolver doesn't work in the default case, since the
            // actual BidirectionalDictionary<string, object> mappings are held in the 
            // JsonSerializerInternalBase.
            // See https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/Serialization/DefaultReferenceResolver.cs
            ReferenceResolverProvider = () => serializer.ReferenceResolver,
            PreserveReferencesHandling = serializer.PreserveReferencesHandling,
            StringEscapeHandling = serializer.StringEscapeHandling,
            TraceWriter = serializer.TraceWriter,
            TypeNameHandling = serializer.TypeNameHandling,
            // Changes in Json.NET 10.0.1
            //TypeNameAssemblyFormat was obsoleted and replaced with TypeNameAssemblyFormatHandling in Json.NET 10.0.1
            //TypeNameAssemblyFormat = serializer.TypeNameAssemblyFormat,
            TypeNameAssemblyFormatHandling = serializer.TypeNameAssemblyFormatHandling,
            //Binder was obsoleted and replaced with SerializationBinder in Json.NET 10.0.1
            //Binder = serializer.Binder,
            SerializationBinder = serializer.SerializationBinder,
        };
        return settings;
    }
}

public static class StackExtensions
{
    public struct PushValue<T> : IDisposable
    {
        readonly Stack<T> stack;

        public PushValue(T value, Stack<T> stack)
        {
            this.stack = stack;
            stack.Push(value);
        }

        // By using a disposable struct we avoid the overhead of allocating and freeing an instance of a finalizable class.
        public void Dispose()
        {
            if (stack != null)
                stack.Pop();
        }
    }

    public static PushValue<T> PushUsing<T>(this Stack<T> stack, T value)
    {
        if (stack == null)
            throw new ArgumentNullException();
        return new PushValue<T>(value, stack);
    }
}

然后像这样使用它:

public class RootObject
{
    public string Name { get; set; }
    public DateTime DateCreated { get; set; }

    [JsonProperty(NamingStrategyType = typeof(DefaultNamingStrategy))]
    [JsonConverter(typeof(AlternateContractResolverConverter), typeof(DefaultContractResolver))]
    public SomeDocument SomeDocument { get; set; }
}

public class SomeDocument
{
    public string MyFirstProperty { get; set; }
    public string mysecondPROPERTY { get; set; }
    public AnotherRandomSubdoc another_random_subdoc { get; set; }
}

public class AnotherRandomSubdoc
{
    public string evenmoredata { get; set; }
    public DateTime DateCreated { get; set; }
}

(这里我假设您希望逐字序列化 "SomeDocument" 属性名称，即使您的问题并不完全清楚。为此，我使用 JsonPropertyAttribute.NamingStrategyType 来自Json.NET 9.0.1。如果您使用的是早期版本，则需要明确设置属性名称。)

那么生成的 JSON 将是:

{
  "name": "Question 40597532",
  "dateCreated": "2016-11-14T05:00:00Z",
  "SomeDocument": {
    "MyFirstProperty": "my first property",
    "mysecondPROPERTY": "my second property",
    "another_random_subdoc": {
      "evenmoredata": "even more data",
      "DateCreated": "2016-11-14T05:00:00Z"
    }
  }
}

请注意，此解决方案不适用于 preserving object references 。如果您需要它们一起工作，您可能需要考虑一种基于堆栈的方法，类似于 Json.NET serialize by depth and attribute 中的方法

演示 fiddle here 。

顺便说一句，您是否考虑过将此 JSON 存储为原始字符串文字，如 this question 的答案？