Mongo C＃Driver 2.0聚合组例外

Question

我尝试使用流畅的Aggregate界面，根据多字段键为每个组选择集合中的最新记录：

        var matches = await Collection.Aggregate()
            .Match(x => x.EffectiveDate >= minEffectiveDate)
            .SortByDescending(x => x.LastUpdate)
            .Group(key => new { key.EffectiveDate, key.ProductOid, key.InstrumentParentOid, key.ComponentOid, key.EventSummary }, g => g.First())
            .ToListAsync();

但是，我得到以下例外：

System.InvalidCastException occurred
  HResult=-2147467262
  Message=Unable to cast object of type 'MongoDB.Driver.Linq.Expressions.SerializationExpression' to type 'System.Linq.Expressions.MethodCallExpression'.
  Source=MongoDB.Driver
  StackTrace:
   at MongoDB.Driver.Linq.Processors.GroupSerializationInfoBinder.GetBodyFromSelector(MethodCallExpression node)
   at MongoDB.Driver.Linq.Processors.GroupSerializationInfoBinder.GetAggregationArgument(MethodCallExpression node)
   at MongoDB.Driver.Linq.Processors.GroupSerializationInfoBinder.VisitMethodCall(MethodCallExpression node)
   at MongoDB.Driver.Linq.Translators.AggregateProjectionTranslator.BindSerializationInfo(SerializationInfoBinder binder, LambdaExpression node, IBsonSerializer parameterSerializer)
   at MongoDB.Driver.Linq.Translators.AggregateProjectionTranslator.TranslateGroup[TKey,TDocument,TResult](Expression`1 idProjector, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.IAggregateFluentExtensions.GroupExpressionProjection`3.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.AggregateFluent`2.<>c__DisplayClass1`1.<Group>b__0(IBsonSerializer`1 s, IBsonSerializerRegistry sr)
   at MongoDB.Driver.DelegatedPipelineStageDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.PipelineStageDefinition`2.MongoDB.Driver.IPipelineStageDefinition.Render(IBsonSerializer inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.PipelineStagePipelineDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.MongoCollectionImpl`1.<AggregateAsync>d__7`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.IAsyncCursorSourceExtensions.<ToListAsync>d__14`1.MoveNext()

确定。因此出于某种原因，它不喜欢IEnumerable扩展方法。所以我尝试提取LINQ扩展方法：

        var matches = await Collection.Aggregate()
            .Match(x => x.EffectiveDate >= minEffectiveDate)
            .SortByDescending(x => x.LastUpdate)
            .Group(key => new { key.EffectiveDate, key.ProductOid, key.InstrumentParentOid, key.ComponentOid, key.EventSummary }, g => g)
            .ToListAsync();
        return matches.Select(x => x.First());

可是：

System.InvalidCastException occurred
  HResult=-2147467262
  Message=Unable to cast object of type 'MongoDB.Bson.Serialization.Serializers.ArraySerializer`1[SPMO.Providers.Audit.Messages.ProductAdjustmentAuditDataDb]' to type 'MongoDB.Bson.Serialization.IBsonSerializer`1[System.Linq.IGrouping`2[<>f__AnonymousType0`5[System.Nullable`1[System.DateTime],System.Nullable`1[System.Int32],System.Nullable`1[System.Int32],System.Nullable`1[System.Int32],System.String],SPMO.Providers.Audit.Messages.ProductAdjustmentAuditDataDb]]'.
  Source=MongoDB.Driver
  StackTrace:
       at MongoDB.Driver.Linq.Translators.AggregateProjectionTranslator.TranslateGroup[TKey,TDocument,TResult](Expression`1 idProjector, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, IBsonSerializerRegistry serializerRegistry)
       at MongoDB.Driver.IAggregateFluentExtensions.GroupExpressionProjection`3.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
       at MongoDB.Driver.AggregateFluent`2.<>c__DisplayClass1`1.<Group>b__0(IBsonSerializer`1 s, IBsonSerializerRegistry sr)
       at MongoDB.Driver.DelegatedPipelineStageDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
       at MongoDB.Driver.PipelineStageDefinition`2.MongoDB.Driver.IPipelineStageDefinition.Render(IBsonSerializer inputSerializer, IBsonSerializerRegistry serializerRegistry)
       at MongoDB.Driver.PipelineStagePipelineDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
       at MongoDB.Driver.MongoCollectionImpl`1.<AggregateAsync>d__7`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.IAsyncCursorSourceExtensions.<ToListAsync>d__14`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.Runtime.CompilerServices.TaskAwaiter`1.GetResult()

我的计划B只是忘记Aggregate，做一个简单的Find（）然后在vanilla LINQ中做一个GroupBy（），但是我想让它在DB上工作，因为它会更有效率。