Mongo C# 驱动程序 2.0 聚合组异常

Question

我正在尝试使用流畅的聚合接口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，我得到以下异常：

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()

还行。因此，由于某种原因，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());

但：

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（），但我想让它在数据库上工作，因为它会更有效率。

Answer 1

我遇到了同样的问题。 我的解决方法是不同的：我不使用 LINQ GroupBy（） 客户端，而是进行两次服务器调用。

1. 获取我希望检索的文档的MongoDB ObjectId，即我希望Group（）简单地作为POCO为我发出的文档。
2. 使用 Contains（） 对步骤 1 中的 ObjectId 集合执行 Find（）。

演示这一点的代码

public static class WidgetWorker
{
    public static void Main()
    {
        //setup
        var widgetCollection = new MongoClient("mongodb://localhost:27017")
            .GetDatabase("WidgetDatabase")
            .GetCollection<Widget>("Widget");
        widgetCollection.DeleteManyAsync(x => true).Wait();   //remove all existing rows
        //create widgets and add to DB;  2 SKUs, each with multiple revisions
        var widgetA1 = new Widget() { SKU = "aaaa", Revision = 1M, Cost = 10 };
        var widgetA2 = new Widget() { SKU = "aaaa", Revision = 2.1M, Cost = 20 };
        var widgetA3 = new Widget() { SKU = "aaaa", Revision = 2.2M, Cost = 30 };
        var widgetB1 = new Widget() { SKU = "bbbb", Revision = 1M, Cost = 40 };
        var widgetB2 = new Widget() { SKU = "bbbb", Revision = 1.1M, Cost = 50 };
        widgetCollection.InsertManyAsync(new[] { widgetA1, widgetA2, widgetA3, widgetB1, widgetB2 }).Wait();
        //get the ObjectId of the most Recent revision of each SKU
        var r = widgetCollection
            .Aggregate()
            .SortByDescending(x => x.Revision)
            .Group(x => x.SKU, g => new { Id = g.First().Id })
            .ToListAsync()
            .Result;
        //get the Widget objects for the list of ids just collected
        var ids = r.Select(x => x.Id).ToArray();
        var widgets = widgetCollection
            .Find(x => ids.Contains(x.Id))
            .ToListAsync()
            .Result;
        //check results
        Debug.Assert(widgets.Count() == 2);
        Debug.Assert(widgets.Single(x => x.SKU == "aaaa").Revision == 2.2M);
        Debug.Assert(widgets.Single(x => x.SKU == "bbbb").Revision == 1.1M);
    }
}
public class Widget
{
    [BsonId]
    public ObjectId Id { get; set; }
    public string SKU { get; set; }
    public decimal Revision { get; set; }
    public decimal Cost { get; set; }
}