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我在 MongoDB 中反序列化 TwitterStatus 类时遇到以下问题，这是使用 MongoDB C# 驱动程序 1.8.0.124 和 TweetSharp 2.0 的失败单元测试：

using Microsoft.VisualStudio.TestTools.UnitTesting;
using MongoDB.Driver;
using MongoDB.Driver.Builders;
using System.Linq;
using TweetSharp;

namespace DS.Model.Tests
{
    [TestClass]
    public class TestMongoSerialization
    {
        [TestMethod]
        public void CanDeserializeTwitterEntitiesFromMongoDB()
        {
            var server = new MongoClient().GetServer();
            MongoDatabase db = server.GetDatabase("test");
            var tweets = db.GetCollection<TwitterStatus>("tweetSerialized");

            var tweet = Newtonsoft.Json.JsonConvert.DeserializeObject<TwitterStatus>(tweetWithTwitterEntityiesSerialized);
            Assert.AreEqual(1, tweet.Entities.Count());
            Assert.AreEqual(TwitterEntityType.Url, tweet.Entities.First().EntityType);
            tweets.Save(tweet);
            Assert.AreEqual(1, tweets.FindAll().Count()); 

            var tweetFromMango = tweets.FindOne(Query<TwitterStatus>.EQ(s => s.Id, 315278676398858240));
            Assert.AreEqual(TwitterEntityType.Url, tweetFromMango.Entities.First().EntityType); // throws exception [1]
        }

        string tweetWithTwitterEntityiesSerialized = @"{""Id"":315278676398858240,""Text"":""TeePublic Funds 22 Designs "",""RetweetedStatus"":null,""created_at"":""2013-03-23T01:47:48Z"",""geo"":null,""Entities"":{""user_mentions"":[],""hashtags"":[],""urls"":[{""url"":""http://t.co/rBGN46rua7"",""expanded_url"":""http://zite.to/10uCED9"",""indices"":[71,93],""EntityType"":2}],""media"":[]},""possibly_sensitive"":false,""Place"":null}";

    }
}

抛出的异常是Enumerable class TwitterEntities does not implement ICollection<T> so it can't be deserialized，下面的完整堆栈跟踪。

完整的堆栈跟踪：

System.IO.FileFormatException: An error occurred while deserializing the Entities property of class TweetSharp.TwitterStatus: 
Enumerable class TwitterEntities does not implement ICollection<T> so it can't be deserialized. ---> MongoDB.Bson.BsonSerializationException: Enumerable class TwitterEntities does not implement ICollection<T> so it can't be deserialized.
Result StackTrace:  
at MongoDB.Bson.Serialization.Serializers.EnumerableSerializer`1.CreateInstance(Type type)
   at MongoDB.Bson.Serialization.Serializers.EnumerableSerializer`1.Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options)
   at MongoDB.Bson.Serialization.BsonClassMapSerializer.DeserializeMemberValue(BsonReader bsonReader, BsonMemberMap memberMap)
 --- End of inner exception stack trace ---
    at MongoDB.Bson.Serialization.BsonClassMapSerializer.DeserializeMemberValue(BsonReader bsonReader, BsonMemberMap memberMap)
   at MongoDB.Bson.Serialization.BsonClassMapSerializer.Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options)
   at MongoDB.Bson.Serialization.BsonClassMapSerializer.Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options)
   at MongoDB.Bson.Serialization.BsonSerializer.Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options)

如果没有此异常，如何从 mongoDB 反序列化 TweetStatus 类？作为参考，有TwitterEntity 类

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1 回答 1

2

TwitterStatus 有一个属性

public virtual TwitterEntities Entities

它被定义为

public class TwitterEntities : IEnumerable<TwitterEntity>

现在，当反序列化 JSon.NET 时，会创建一个 TwitterEntities 实例，然后尝试用TwitterEntity项填充它。但要做到这一点，它需要一个 Add 方法，而IEnumerable没有提供。但是ICollection(T)确实提供了Add方法，这就是它要求 ICollection(T) 的原因。

但是，如果您使用的是 MongoDb IMO，则不应直接进行任何 JSON 转换。您应该只有简单的 POCO 类，MongoDb 驱动程序会自动为您处理这些类实例的（反）序列化。

这就是使用文档数据库的美妙之处。

于 2013-03-24T20:24:20.220 回答