MongoDB数据实体中的ObjectId序列化成json的一个小坑

　　很多时候我们都需要对实体对象进行序列化与反序列化,而ObjectId类型,只能用mongo的驱动以bson格式来序列化,但我们对外的交互,一般是json格式.

有两种解决方案:

　　1.自己写一个json.net的ObjectIdConverter来针对ObjectId,适用于json.net

　　2.增加string类型的中间变量IdStr ,优点是适用于所有情况,比如mvc自带的序列化工具等

测试代码如下:

  [TestClass]
     public class MongoTest
     {
         [TestMethod()]
         public void Temp1()
         {
             var entity = new MyEntity()
             {
                 Id = new ObjectId("555afe4204cbee061cc31b6f"),
                 Name = "ZhangSan"
             };
             var str = JsonConvert.SerializeObject(entity);//{"Id":"555afe4204cbee061cc31b6f","Name":"ZhangSan"}
             var entity1 = JsonConvert.DeserializeObject<MyEntity>(str);
         }

         [TestMethod()]
         public void Temp2()
         {
             var entity = new MyEntity2()
             {
                 Id = new ObjectId("555afe4204cbee061cc31b6f"),
                 Name = "ZhangSan"
             };
             var str = JsonConvert.SerializeObject(entity); //{"IdStr":"555afe4204cbee061cc31b6f","Name":"ZhangSan"}
             var entity2 = str.FromJson<MyEntity2>();
         }

         [TestMethod()]
         public void Temp3()
         {
             var entity = new MyEntity3()
             {
                 Id = new ObjectId("555afe4204cbee061cc31b6f"),
                 Name = "ZhangSan"
             };
             var str = JsonConvert.SerializeObject(entity); //{"Id":"555afe4204cbee061cc31b6f","Name":"ZhangSan"}
             var entity2 = str.FromJson<MyEntity3>();
         }
     }

     public class MyEntity
     {
         public virtual ObjectId Id { get; set; }
         public virtual string Name { get; set; }
     }

     public class MyEntity2 : MyEntity
     {
         [JsonIgnore]
         public override  ObjectId Id { get; set; }

         [BsonIgnore]
         public string IdStr
         {
             get
             {
                 return Id.ToString();
             }
             set
             {
                 ObjectId id;
                 ObjectId.TryParse(value, out id);
                 Id = id;
             }
         }
     }

     public class MyEntity3 : MyEntity
     {
         [JsonConverter(typeof(ObjectIdConverter))]
         public override ObjectId Id { get; set; }
     }
     public class ObjectIdConverter : 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 parsing ObjectId. Expected String, got {0}.",
                                   reader.TokenType));
             }

             var 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)
             {
                 var objectId = (ObjectId)value;

                 writer.WriteValue(objectId != ObjectId.Empty ? objectId.ToString() : String.Empty);
             }
             else
             {
                 throw new Exception("Expected ObjectId value.");
             }
         }
     }