我可以在属性中指定路径以将我的类中的属性映射到我的JSON中的子属性吗？

Question

有些代码(我无法更改)使用Newtonsoft.Json DeserializeObject<T>(strJSONData)从Web请求中获取数据并将其转换为类对象(我可以更改类).通过使用我的类属性进行装饰,[DataMember(Name = "raw_property_name")]我可以将原始JSON数据映射到我的类中的正确属性.有没有办法可以将JSON复杂对象的子属性映射到一个简单的属性？这是一个例子:

{
    "picture": 
    {
        "id": 123456,
        "data": 
        {
            "type": "jpg",
            "url": "http://www.someplace.com/mypicture.jpg"
        }
    }
}

除了URL之外,我不关心任何其他图片对象,因此不想在我的C#类中设置复杂对象.我真的只想要这样的东西:

[DataMember(Name = "picture.data.url")]
public string ProfilePicture { get; set; }

这可能吗？

Answer 1

好吧,如果你只需要一个额外的属性,一个简单的方法是将你的JSON解析为a JObject,ToObject()用来填充你的类JObject,然后用来SelectToken()引入额外的属性.

所以,假设你的课看起来像这样:

class Person
{
    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("age")]
    public string Age { get; set; }

    public string ProfilePicture { get; set; }
}

你可以这样做:

string json = @"
{
    ""name"" : ""Joe Shmoe"",
    ""age"" : 26,
    ""picture"":
    {
        ""id"": 123456,
        ""data"":
        {
            ""type"": ""jpg"",
            ""url"": ""http://www.someplace.com/mypicture.jpg""
        }
    }
}";

JObject jo = JObject.Parse(json);
Person p = jo.ToObject<Person>();
p.ProfilePicture = (string)jo.SelectToken("picture.data.url");

小提琴:https://dotnetfiddle.net/7gnJCK

如果您更喜欢更实用的解决方案,则可以进行自定义JsonConverter以使该JsonProperty属性的行为与您描述的相似.转换器需要在类级别操作,并使用一些反射结合上述技术来填充所有属性.这是代码中的样子:

class JsonPathConverter : JsonConverter
{
    public override object ReadJson(JsonReader reader, Type objectType, 
                                    object existingValue, JsonSerializer serializer)
    {
        JObject jo = JObject.Load(reader);
        object targetObj = Activator.CreateInstance(objectType);

        foreach (PropertyInfo prop in objectType.GetProperties()
                                                .Where(p => p.CanRead && p.CanWrite))
        {
            JsonPropertyAttribute att = prop.GetCustomAttributes(true)
                                            .OfType<JsonPropertyAttribute>()
                                            .FirstOrDefault();

            string jsonPath = (att != null ? att.PropertyName : prop.Name);
            JToken token = jo.SelectToken(jsonPath);

            if (token != null && token.Type != JTokenType.Null)
            {
                object value = token.ToObject(prop.PropertyType, serializer);
                prop.SetValue(targetObj, value, null);
            }
        }

        return targetObj;
    }

    public override bool CanConvert(Type objectType)
    {
        // CanConvert is not called when [JsonConverter] attribute is used
        return false;
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value,
                                   JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

为了演示,让我们假设JSON现在如下所示:

{
  "name": "Joe Shmoe",
  "age": 26,
  "picture": {
    "id": 123456,
    "data": {
      "type": "jpg",
      "url": "http://www.someplace.com/mypicture.jpg"
    }
  },
  "favorites": {
    "movie": {
      "title": "The Godfather",
      "starring": "Marlon Brando",
      "year": 1972
    },
    "color": "purple"
  }
}

...除了之前的信息之外,您还对这个人最喜欢的电影(标题和年份)和喜欢的颜色感兴趣.您首先要使用[JsonConverter]属性标记目标类,以将其与自定义转换器关联,然后[JsonProperty]在每个属性上使用属性,并指定所需的属性路径(区分大小写)作为名称.目标属性也不必是原语 - 你可以像我在这里一样使用子类Movie(并注意不需要介入Favorites类).

[JsonConverter(typeof(JsonPathConverter))]
class Person
{
    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("age")]
    public int Age { get; set; }

    [JsonProperty("picture.data.url")]
    public string ProfilePicture { get; set; }

    [JsonProperty("favorites.movie")]
    public Movie FavoriteMovie { get; set; }

    [JsonProperty("favorites.color")]
    public string FavoriteColor { get; set; }
}

// Don't need to mark up these properties because they are covered by the 
// property paths in the Person class
class Movie
{
    public string Title { get; set; }
    public int Year { get; set; }
}

有了所有属性,您可以正常反序列化,它应该"正常工作":

Person p = JsonConvert.DeserializeObject<Person>(json);

小提琴:https://dotnetfiddle.net/Ljw32O

Answer 2

标记的答案不是100%完成,因为它忽略了可能注册的任何IContractResolver,例如CamelCasePropertyNamesContractResolver等.

同样返回false for can convert会阻止其他用户案例,所以我将其更改为 return objectType.GetCustomAttributes(true).OfType<JsonPathConverter>().Any();

这是更新版本:https: //dotnetfiddle.net/F8C8U8

我还删除了JsonProperty在链接中说明的设置属性的需要.

如果由于某种原因上面的链接死亡或爆炸,我还包括以下代码:

public class JsonPathConverter : JsonConverter
    {
        /// <inheritdoc />
        public override object ReadJson(
            JsonReader reader,
            Type objectType,
            object existingValue,
            JsonSerializer serializer)
        {
            JObject jo = JObject.Load(reader);
            object targetObj = Activator.CreateInstance(objectType);

            foreach (PropertyInfo prop in objectType.GetProperties().Where(p => p.CanRead && p.CanWrite))
            {
                JsonPropertyAttribute att = prop.GetCustomAttributes(true)
                                                .OfType<JsonPropertyAttribute>()
                                                .FirstOrDefault();

                string jsonPath = att != null ? att.PropertyName : prop.Name;

                if (serializer.ContractResolver is DefaultContractResolver)
                {
                    var resolver = (DefaultContractResolver)serializer.ContractResolver;
                    jsonPath = resolver.GetResolvedPropertyName(jsonPath);
                }

                if (!Regex.IsMatch(jsonPath, @"^[a-zA-Z0-9_.-]+$"))
                {
                    throw new InvalidOperationException($"JProperties of JsonPathConverter can have only letters, numbers, underscores, hiffens and dots but name was ${jsonPath}."); // Array operations not permitted
                }

                JToken token = jo.SelectToken(jsonPath);
                if (token != null && token.Type != JTokenType.Null)
                {
                    object value = token.ToObject(prop.PropertyType, serializer);
                    prop.SetValue(targetObj, value, null);
                }
            }

            return targetObj;
        }

        /// <inheritdoc />
        public override bool CanConvert(Type objectType)
        {
            // CanConvert is not called when [JsonConverter] attribute is used
            return objectType.GetCustomAttributes(true).OfType<JsonPathConverter>().Any();
        }

        /// <inheritdoc />
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            var properties = value.GetType().GetRuntimeProperties().Where(p => p.CanRead && p.CanWrite);
            JObject main = new JObject();
            foreach (PropertyInfo prop in properties)
            {
                JsonPropertyAttribute att = prop.GetCustomAttributes(true)
                    .OfType<JsonPropertyAttribute>()
                    .FirstOrDefault();

                string jsonPath = att != null ? att.PropertyName : prop.Name;

                if (serializer.ContractResolver is DefaultContractResolver)
                {
                    var resolver = (DefaultContractResolver)serializer.ContractResolver;
                    jsonPath = resolver.GetResolvedPropertyName(jsonPath);
                }

                var nesting = jsonPath.Split('.');
                JObject lastLevel = main;

                for (int i = 0; i < nesting.Length; i++)
                {
                    if (i == nesting.Length - 1)
                    {
                        lastLevel[nesting[i]] = new JValue(prop.GetValue(value));
                    }
                    else
                    {
                        if (lastLevel[nesting[i]] == null)
                        {
                            lastLevel[nesting[i]] = new JObject();
                        }

                        lastLevel = (JObject)lastLevel[nesting[i]];
                    }
                }
            }

            serializer.Serialize(writer, main);
        }
    }

Answer 3

坚持做

lastLevel [nesting [i]] = new JValue(prop.GetValue (value));

你必须做

lastLevel[nesting[i]] = JValue.FromObject(jValue);

否则我们有一个

无法确定类型的JSON对象类型...

例外

一段完整的代码将是这样的:

object jValue = prop.GetValue(value);
if (prop.PropertyType.IsArray)
{
    if(jValue != null)
        //https://stackoverflow.com/a/20769644/249895
        lastLevel[nesting[i]] = JArray.FromObject(jValue);
}
else
{
    if (prop.PropertyType.IsClass && prop.PropertyType != typeof(System.String))
    {
        if (jValue != null)
            lastLevel[nesting[i]] = JValue.FromObject(jValue);
    }
    else
    {
        lastLevel[nesting[i]] = new JValue(jValue);
    }                               
}

Answer 4

如果有人需要使用@BrianRogers的JsonPathConverter还与WriteJson选择,这里有一个解决方案(即仅适用于具有路径作品只点):

删除该CanWrite属性,以便它true再次成为默认值.

用WriteJson以下代码替换代码:

public override void WriteJson(JsonWriter writer, object value,
    JsonSerializer serializer)
{
    var properties = value.GetType().GetRuntimeProperties ().Where(p => p.CanRead && p.CanWrite);
    JObject main = new JObject ();
    foreach (PropertyInfo prop in properties) {
        JsonPropertyAttribute att = prop.GetCustomAttributes(true)
            .OfType<JsonPropertyAttribute>()
            .FirstOrDefault();

        string jsonPath = (att != null ? att.PropertyName : prop.Name);
        var nesting=jsonPath.Split(new[] { '.' });
        JObject lastLevel = main;
        for (int i = 0; i < nesting.Length; i++) {
            if (i == nesting.Length - 1) {
                lastLevel [nesting [i]] = new JValue(prop.GetValue (value));
            } else {
                if (lastLevel [nesting [i]] == null) {
                    lastLevel [nesting [i]] = new JObject ();
                }
                lastLevel = (JObject)lastLevel [nesting [i]];
            }
        }

    }
    serializer.Serialize (writer, main);
}

如上所述,这仅适用于包含点的路径.鉴于此,您应该添加以下代码ReadJson以防止其他情况:

[...]
string jsonPath = (att != null ? att.PropertyName : prop.Name);
if (!Regex.IsMatch(jsonPath, @"^[a-zA-Z0-9_.-]+$")) {
    throw new InvalidOperationException("JProperties of JsonPathConverter can have only letters, numbers, underscores, hiffens and dots."); //Array operations not permitted
}
JToken token = jo.SelectToken(jsonPath);
[...]