C# AutoMapperMappingException KeyNotFoundException 异常

Question

我猜测除了异常之外的所有信息都是额外的并且几乎不相关(并且在这里是为了完整性)。问题是:根据下面的异常，到底遇到了什么问题？

我无法理解异常消息。据我所知，将 BsonDocument 映射到 ChildItemViewModel 时出错。 Id、Description 和 SequentialOrgId 已成功映射...然后发生了一些事情，尽管这些是唯一的属性。似乎它正在 cI(正在转换为 ChildItemViewModel 的 BsonDocument)中寻找 _id(一个不存在的属性)，但我不知道这是否正确，因为这没有意义。

这是一段代码(映射)，我相信这会发生，但我不知道，因为我没有行号。

        foreach (BsonDocument cI in childItems)
        {
            ChildItemViewModel childItem = Mapper.Map<BsonDocument, ChildItemViewModel>(cI);
            itemView.ChildItems.Add(childItem);
        }

这是 Entity Framework View 模型(类):

public class ChildItemViewModel
{
    public long Id { get; set; }
    public string Description { get; set; }
    public long SequentialOrgId { get; set; }
}

这是来源:

编辑:我已经确认 ChildItems 字段是问题的根源。如果我用下面的代码清除它们，问题就会消失:

db.items.update(
   { _id: 1245846 },
   { $set:
      {
            "ChildItems":[], 
            "ChildItemsAmount": NumberInt(0)
      }
   }
)

异常:

 {"message":"AutoMapper.AutoMapperMappingException: 

 Mapping types:
 BsonDocument -> Int64
 MongoDB.Bson.BsonDocument -> System.Int64

 Destination path:
 ChildItemViewModel.Id.Id

 Source value:
 { \"Id\" : NumberLong(1245854), \"Description\" : \"Image of Ext USB drive containing backup files labeled \\\"Kevin SomeLastName Backups\\\"\", \"SequentialOrgId\" : NumberLong(189) } ---> System.Collections.Generic.KeyNotFoundException: Element '_id' not found.
    at MongoDB.Bson.BsonDocument.get_Item(String name)
    at lambda_method(Closure , BsonDocument )
    at AutoMapper.Internal.DelegateBasedResolver`2.Resolve(ResolutionResult source)
    at AutoMapper.NullReferenceExceptionSwallowingResolver.Resolve(ResolutionResult source)
    at System.Linq.Enumerable.Aggregate[TSource,TAccumulate](IEnumerable`1 source, TAccumulate seed, Func`3 func)
    at AutoMapper.Mappers.TypeMapObjectMapperRegistry.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap)
    --- End of inner exception stack trace ---
    at AutoMapper.Mappers.TypeMapObjectMapperRegistry.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap)
    at AutoMapper.Mappers.TypeMapObjectMapperRegistry.PropertyMapMappingStrategy.Map(ResolutionContext context, IMappingEngineRunner mapper)
    at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context)
    at AutoMapper.MappingEngine.Map[TSource,TDestination](TSource source)
    at API.Classes.Automapper.ItemViewModelConverter.Convert(ResolutionContext resolution)
    at AutoMapper.Internal.MappingExpression`2.<>c__DisplayClass51_0.<ConvertUsing>b__0(ResolutionContext context)
    at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context)
    at AutoMapper.MappingEngine.Map[TSource,TDestination](TSource source)
    at MongoDB.Bson.Serialization.Serializers.ProjectingDeserializer`2.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
    at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)
    at MongoDB.Driver.Core.WireProtocol.Messages.Encoders.BinaryEncoders.ReplyMessageBinaryEncoder`1.ReadMessage()
    at MongoDB.Driver.Core.Connections.BinaryConnection.<ReceiveMessageAsync>d__15.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.Core.WireProtocol.QueryWireProtocol`1.<ExecuteAsync>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.Core.Servers.ClusterableServer.ServerChannel.<ExecuteProtocolAsync>d__24`1.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.Core.Operations.FindOperation`1.<ExecuteAsync>d__2.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.OperationExecutor.<ExecuteReadOperationAsync>d__0`1.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.MongoCollectionImpl`1.<ExecuteReadOperation>d__35`1.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at MongoDB.Driver.IFindFluentExtensions.<SingleOrDefaultAsync>d__f`2.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at API.Controllers.ItemsController.<GetItem>d__2.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Threading.Tasks.TaskHelpersExtensions.<CastToObject>d__3`1.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__2.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Controllers.AuthenticationFilterResult.<ExecuteAsync>d__0.MoveNext()
 --- End of stack trace from previous location where exception was thrown ---
    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()"}

Answer 1

MongoDB 驱动程序本身就是罪魁祸首。当它遇到 Id 属性时，它会自动假定它需要映射到相应的 _id 字段。为了解决这个问题，你只需要添加一个属性告诉驱动程序你比它更了解:

public class ChildItemViewModel
{
    [BsonElement("Id")]
    public long Id { get; set; }
    public string Description { get; set; }
    public long SequentialOrgId { get; set; }
}

或者，似乎还有 [BsonNoId] 属性，您在类级别应用该属性:

[BsonNoId]
public class ChildItemViewModel