1

我正在尝试按name字段对集合进行分组，并score使用聚合管道获取最大的文档。

public async Task<IEnumerable<Student>> GetTopAsync(int limit, int offset)
{
    var x = await students
        .Aggregate(new AggregateOptions{AllowDiskUse = true})
        .Group(k => k.Class, g => g.OrderByDescending(o => o.Score).First())
        .Skip(offset)
        .Limit(limit)
        .ToListAsync();

    return x;
}

但是，上述方法会引发异常：

2020-11-10 10:57:27.3687|1.0.0.0|d3019991-db73-4a98-b331-ac6f00b49331|GlobalExceptionFilter|System.NotSupportedException: Specified method is not supported.
   at MongoDB.Driver.Linq.Processors.AccumulatorBinder.GetAccumulatorArgument(Expression node)
   at MongoDB.Driver.Linq.Processors.AccumulatorBinder.TryGetAccumulatorTypeAndArgument(PipelineExpression node, AccumulatorType& accumulatorType, Expression& argument)
   at MongoDB.Driver.Linq.Processors.AccumulatorBinder.VisitPipeline(PipelineExpression node)
   at MongoDB.Driver.Linq.Expressions.PipelineExpression.Accept(ExtensionExpressionVisitor visitor)
   at MongoDB.Driver.Linq.Processors.AccumulatorBinder.Bind(Expression node, IBindingContext bindingContext)
   at MongoDB.Driver.Linq.Processors.EmbeddedPipeline.EmbeddedPipelineBinder.Bind(Expression node, IBindingContext parent)
   at MongoDB.Driver.Linq.Processors.SerializationBinder.BindEmbeddedPipeline(MethodCallExpression node)
   at MongoDB.Driver.Linq.Processors.SerializationBinder.VisitMethodCall(MethodCallExpression node)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at MongoDB.Driver.Linq.Processors.SerializationBinder.Visit(Expression node)
   at MongoDB.Driver.Linq.Processors.SerializationBinder.Bind(Expression node, IBindingContext context, Boolean isClientSideProjection)
   at MongoDB.Driver.Linq.Processors.PipelineBindingContext.Bind(Expression node, Boolean isClientSideProjection)
   at MongoDB.Driver.Linq.Processors.PipelineBindingContext.Bind(Expression node)
   at MongoDB.Driver.Linq.Translators.AggregateGroupTranslator.BindGroup[TKey,TDocument,TResult](PipelineBindingContext bindingContext, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, Expression keySelector)
   at MongoDB.Driver.Linq.Translators.AggregateGroupTranslator.Translate[TKey,TDocument,TResult](Expression`1 idProjector, Expression`1 groupProjector, IBsonSerializer`1 parameterSerializer, IBsonSerializerRegistry serializerRegistry, ExpressionTranslationOptions translationOptions)
   at MongoDB.Driver.GroupExpressionProjection`3.Render(IBsonSerializer`1 documentSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.PipelineStageDefinitionBuilder.<>c__DisplayClass19_0`2.<Group>b__0(IBsonSerializer`1 s, IBsonSerializerRegistry sr)
   at MongoDB.Driver.DelegatedPipelineStageDefinition`2.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.AppendedStagePipelineDefinition`3.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.AppendedStagePipelineDefinition`3.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.AppendedStagePipelineDefinition`3.Render(IBsonSerializer`1 inputSerializer, IBsonSerializerRegistry serializerRegistry)
   at MongoDB.Driver.MongoCollectionImpl`1.AggregateAsync[TResult](IClientSessionHandle session, PipelineDefinition`2 pipeline, AggregateOptions options, CancellationToken cancellationToken)
   at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSessionAsync[TResult](Func`2 funcAsync, CancellationToken cancellationToken)
   at MongoDB.Driver.IAsyncCursorSourceExtensions.ToListAsync[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)

我猜驱动程序中没有实现 orderby/first 方法？实现这一目标的最佳方法是什么？

4

0 回答 0