Web api Json 接受的参数类型为父类，自动序列化为子类的过程

场景:

 public abstract class JsonCreationConverter<T> : JsonConverter
    {
        /// <summary>
        /// this is very important, otherwise serialization breaks!
        /// </summary>
        public override bool CanWrite
        {
            get
            {
                return false;
            }
        }
        /// <summary>
        /// Create an instance of objectType, based properties in the JSON object
        /// </summary>
        /// <param name="objectType">type of object expected</param>
        /// <param name="jObject">contents of JSON object that will be
        /// deserialized</param>
        /// <returns></returns>
        protected abstract T Create(Type objectType, JObject jObject);

        public override bool CanConvert(Type objectType)
        {
            return typeof(T).IsAssignableFrom(objectType);
        }

        public override object ReadJson(JsonReader reader, Type objectType,
          object existingValue, JsonSerializer serializer)
        {
            if (reader.TokenType == JsonToken.Null)
                return null;
            // Load JObject from stream
            JObject jObject = JObject.Load(reader);

            // Create target object based on JObject
            T target = Create(objectType, jObject);

            // Populate the object properties
            serializer.Populate(jObject.CreateReader(), target);

            return target;
        }

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

  [JsonConverter(typeof(UserConverter))]
    public class User
    {

        private class UserConverter : JsonCreationConverter<User>
        {
            protected override User Create(Type objectType, Newtonsoft.Json.Linq.JObject jObject)
            {
                if (jObject.Property("Course") !=null)
                {
                    return new Student();
                }
                else if (jObject.Property("WorkerType") != null)
                {
                    return new Worker();
                }
                else
                {
                    return new User ();
                }
            }
        }

        public string Name { get; set; }
        public int Id { get; set; }
    }

    public class Student : User
    {
        public string Course { get; set; }
    }

    public class Worker : User
    {
        public string WorkerType { get; set; }
    }

        [Route("api/Employee/AddUsers/")]
        public void AddUsers(List<User> users)
        {

            User s = users[] as User;
            Student s1= users[] as Student;
            Worker s2 = users[] as Worker;

            s1 = users[] as Student;
            if (s1 != null)
            {

            }
            //[{"Name":"1","Id":1},{"Course":"2","Name":"2","Id":2},{"WorkerType":"3","Name":"3","Id":3}]
        }