Servers.Core库中实现MongoDB的ObjectId和Json转换

        这个是个转换的工具类，主要目的是把C#中的ObjectId类转换成Json格式，Json抓换成Mongo的ObjectId，相当于是个序列化反序列化的过程。在以后的接收和发送数据的时候需要用到。

代码：

using MongoDB.Bson;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Text;

namespace Servers.Core
{
    //MongoDB的ObjectId 2 Json转换
    public class YFObjectIdConverter : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(ObjectId);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (reader.TokenType != JsonToken.String)
            {
                throw new Exception(string.Format("Unexpected token parsring ObjectId. Expected String,got{0}", reader.TokenType));
            }

            string value = (string)reader.Value;
            return String.IsNullOrEmpty(value) ? ObjectId.Empty : new ObjectId(value);
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            if (value is ObjectId)
            {
                ObjectId objectId = (ObjectId)value;
                writer.WriteValue(objectId != ObjectId.Empty ? objectId.ToString() : string.Empty);
            }
            else
            {
                throw new Exception("Expected ObjectId value.");
            }
        }
    }
}