使用Json.NET将JSON反序列化为对象

Question

I'm playing a little bit with the new StackOverflow API . Unfortunately, my JSON is a bit weak, so I need some help.

I'm trying to deserialize this JSON of a User:

  {"user":{
    "user_id": 1,
    "user_type": "moderator",
    "creation_date": 1217514151,
    "display_name": "Jeff Atwood",
    ...
    "accept_rate": 100
  }}

into an object which I've decorated with JsonProperty attributes:

[JsonObject(MemberSerialization.OptIn)]
public class User
{
    [JsonProperty("user_id", Required = Required.Always)]        
    public virtual long UserId { get; set; }

    [JsonProperty("display_name", Required = Required.Always)]
    public virtual string Name { get; set; }

    ...
}

I get the following exception:

Newtonsoft.Json.JsonSerializationException: Required property 'user_id' not found in JSON.

Is this because the JSON object is an array? If so, how can I deserialize it to the one User object?

Thanks in advance!

Answer 1

If you don't want to create a wrapper class you can also access the User this way:

String jsonString = "{\"user\":{\"user_id\": 1, \"user_type\": \"moderat...";
JToken root = JObject.Parse(jsonString);
JToken user = root["user"];
User deserializedUser = JsonConvert.DeserializeObject<User>(user.ToString());

See this page in the Json.NET doc for details.

Answer 2

As Alexandre Jasmin said in the comments of your question, the resulting JSON has a wrapper around the actual User object you're trying to deserialize.

A work-around would be having said wrapper class:

public class UserResults
{
    public User user { get; set; }
}

Then the deserialization will work:

using (var sr = new StringReader(json))
using (var jr = new JsonTextReader(sr))
{
    var js = new JsonSerializer();
    var u = js.Deserialize<UserResults>(jr);
    Console.WriteLine(u.user.display_name);
}

There will be future metadata properties on this wrapper, eg response timestamp, so it's not a bad idea to use it!

Answer 3

Similar to @Alexandre Jasmin's answer , you can use an intermediary JsonSerializer to convert instead of the using the high-level JsonConvert on .ToString() . No idea if it's any more efficient...

References:

• https://stackoverflow.com/a/9453198/1037948
• http://www.west-wind.com/weblog/posts/2012/Aug/30/Using-JSONNET-for-dynamic-JSON-parsing

Example:

var root = JObject.Parse(jsonString);
var serializer = new JsonSerializer();
var expectedUserObject = serializer.Deserialize<User>(root["user"].CreateReader());