[英]C# MongoDB & Projection. Fails with serialization Exception
Let's say I have a collection like : 假设我有一个类似的收藏:
{
id: "1"
name: "collection 1"
properties: "Some properties."
}
With a class representation as 以类表示为
[BsonIgnoreExtraElements]
public class InfoPOCO {
[BsonRepresentation(BsonType.ObjectId)]
public string Id { get; set; }
[BsonElement("name")]
public string Name { get; set; }
[BsonElement("properties")]
public string Properties { get; set; }
}
Now if am going to create a Projection like 现在,如果要创建一个像
Builders<InfoPOCO>.Projection.Include(_ => new{_.Name});
And call it with other params ( That is working fine without projection ) 并与其他参数一起调用(无需投影即可正常工作)
return GetDataBase().GetCollection<InfoPOCO>(collectionName).Find(Expr).
Project<InfoPOCO>(projectionDefinition).Skip(Offset).Limit(Limit).Sort(sort).ToList<InfoPOCO>()
Then I get the following error: 然后我得到以下错误:
System.InvalidOperationException : Unable to determine the serialization information for
_ => new <>f__AnonymousType2`1
Result StackTrace:
at MongoDB.Driver.ExpressionFieldDefinition`1.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.SingleFieldProjectionDefinition`1.Render(IBsonSerializer`1 sourceSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.KnownResultTypeProjectionDefinitionAdapter`2.Render(IBsonSerializer`1 sourceSerializer, IBsonSerializerRegistry serializerRegistry)
at MongoDB.Driver.MongoCollectionImpl`1.CreateFindOperation[TProjection](FilterDefinition`1 filter, FindOptions`2 options)
at MongoDB.Driver.MongoCollectionImpl`1.FindSync[TProjection](IClientSessionHandle session, FilterDefinition`1 filter, FindOptions`2 options, CancellationToken cancellationToken)
at MongoDB.Driver.MongoCollectionImpl`1.<>c__DisplayClass35_0`1.<FindSync>b__0(IClientSessionHandle session)
at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSession[TResult](Func`2 func, CancellationToken cancellationToken)
at MongoDB.Driver.MongoCollectionImpl`1.FindSync[TProjection](FilterDefinition`1 filter, FindOptions`2 options, CancellationToken cancellationToken)
at MongoDB.Driver.FindFluent`2.ToCursor(CancellationToken cancellationToken)
at MongoDB.Driver.IAsyncCursorSourceExtensions.ToList[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)
What could be the reason for it, when am not using projection, it is fetching the entire collection fine. 可能的原因是,当不使用投影时,它会提取整个集合。 I don't know if I need to map the classes?
我不知道是否需要映射类吗? (Thought Auto Map would take it) .
(认为自动地图会接受)。 I tried making the constructor in the class too.
我也尝试在类中构造构造函数。 But still the same error.
但是还是一样的错误。 Any help would be highly appreciated.
任何帮助将不胜感激。 Thank you !
谢谢 !
I finally understood! 我终于明白了! Yeah, I know, kinda slow, duh.
是的,我知道,有点慢,du。
The issue is that when I was trying to map it like : 问题是,当我尝试将其映射为:
Builders<InfoPOCO>.Projection.Include(_ => new{_.Name, _.Properties});
It's a strongly typed expression and the result is mapped to an anonymous type. 这是一个强类型的表达式,结果被映射到一个匿名类型。 If am using forEach at the same time as am fetching it, then I can get those values.
如果在获取时同时使用forEach,那么我可以获得这些值。 So the solution I am using right now is simple.
因此,我现在使用的解决方案很简单。 I changed my projection to:
我将投影更改为:
Builders<InfoPOCO>.Projection.Include(_ => _.Name).
Include(_ => _.Properties);
This works! 这可行! Am not saying its the perfect solution or explanation but I see a lot of people struggling with it, so just mentioning a workaround.
并不是说它是完美的解决方案或解释,但我看到很多人都在为之苦苦挣扎,所以只提一个解决方法。 Hope it helps someone like me from going through hours of googling!
希望它可以帮助像我这样的人避免经过数小时的谷歌搜索!
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