Linq to SQL：查询在 SQL Server Management Studio 中运行良好，但在应用程序上超时

Question

我正在维护旧版应用程序的代码。它正在使用 Entity Framework 3.5，目前无法将其更新到较新的版本。

最近有一个查询开始超时。这是 LINQ 中的查询：

var compoQueryResult = (from composition in MyAppDataContext.Compositions
                            join compositionStatus in MyAppDataContext.CompositionStatus on composition.StatusID equals compositionStatus.CompositionStatusID
                            join compoUnit in MyAppDataContext.CompositionUnits on composition.CompositionID equals compoUnit.CompositionID
                            join unit in MyAppDataContext.Units on compoUnit.UnitID equals unit.UnitID
                            join carUnit in MyAppDataContext.Car_Units on unit.UnitID equals carUnit.UnitId
                            join car in MyAppDataContext.Cars on carUnit.CarId equals car.CarID
                            join location in MyAppDataContext.Locations on unit.ParkedLocationID equals location.LocationID
                            from road in MyAppDataContext.Roads.Where(r => r.RoadID == unit.RoadID).DefaultIfEmpty()
                            from ta in MyAppDataContext.Allocations.Where(ta => ta.CompositionId == composition.CompositionID).DefaultIfEmpty()
                            from arrivalLocation in MyAppDataContext.Locations.Where(al => al.LocationID == ta.EndLocationID).DefaultIfEmpty()
                            where (MyApp.IsAdministrator || MyApp.GetLineIds().Contains(car.LineId.Value))
                            && car.LineId.Value == LineId                           
                            && (statusId == null || statusId == compositionStatus.CompositionStatusID)
                            && (locationId == null || unit.ParkedLocationID == locationId)
                            && (!onlyATMS.HasValue
                                 || (onlyATMS == true && composition.CompositionName.Contains(Common.Constants.ATMSSymbol))
                                 || (onlyATMS == false && !composition.CompositionName.Contains(Common.Constants.ATMSSymbol)))
                            select new CompositionQueryResultItem
                            {
                                CompositionId = composition.CompositionID,
                                CompositionName = composition.CompositionName,
                                CompositionNumber = composition.CompositionNumber,
                                DateTimeModified = composition.DataModified,
                                Status = compositionStatus.CompositionStatusDesc,
                                Location = location.LocationName,
                                Road = road.Name,
                                Number = ta.Number,
                                DepartureTime = ta.DepartTime,
                                ArrivalLocation = arrivalLocation.LocationName,
                                ArrivalTime = ta.ArriveTime
                            }).Distinct().ToList();

调试应用程序后，我可以看到正在执行以下查询：

SELECT DISTINCT [t10].[CompositionID] AS [CompositionId], [t10].[CompositionName], [t10].[CompositionNumber], [t10].[value] AS [DateTimeModified], [t10].[CompositionStatusDesc] AS [Status], [t10].[LocationName] AS [Location], [t10].[value2] AS [Road], [t10].[value3] AS [Number], [t10].[value4] AS [DepartureTime], [t10].[value5] AS [ArrivalLocation], [t10].[value6] AS [ArrivalTime]
FROM (
    SELECT [t0].[CompositionID], [t0].[CompositionName], [t0].[CompositionNumber], [t0].[DataModified] AS [value], [t1].[CompositionStatusDesc], [t6].[LocationName], [t7].[Name] AS [value2], [t8].[Number] AS [value3], [t8].[DepartTime] AS [value4], [t9].[LocationName] AS [value5], [t8].[ArriveTime] AS [value6], [t5].[LineId]
    FROM [dbo].[Composition] AS [t0]
    INNER JOIN [dbo].[CompositionStatus] AS [t1] ON [t0].[StatusID] = [t1].[CompositionStatusID]
    INNER JOIN [dbo].[CompositionUnit] AS [t2] ON [t0].[CompositionID] = [t2].[CompositionID]
    INNER JOIN [dbo].[Unit] AS [t3] ON [t2].[UnitID] = [t3].[UnitID]
    INNER JOIN [dbo].[Car_Unit] AS [t4] ON [t3].[UnitID] = [t4].[UnitId]
    INNER JOIN [dbo].[Car] AS [t5] ON [t4].[CarId] = [t5].[CarID]
    INNER JOIN [dbo].[Location] AS [t6] ON [t3].[ParkedLocationID] = ([t6].[LocationID])
    LEFT OUTER JOIN [dbo].[Road] AS [t7] ON ([t7].[RoadID]) = [t3].[RoadID]
    LEFT OUTER JOIN [dbo].[Allocation] AS [t8] ON [t8].[CompositionId] = ([t0].[CompositionID])
    LEFT OUTER JOIN [dbo].[Location] AS [t9] ON [t9].[LocationID] = [t8].[EndLocationID]
    ) AS [t10]
WHERE ([t10].[LineId]) = @p0

如果我在 SQL Server Manager Studio 上执行该查询，我根本不会遇到任何问题。它在不到一秒的时间内执行。但是，应用程序正在超时，我不知道为什么。

我试过了

MyAppDataContext.ObjectTrackingEnabled = false;

但我仍然遇到同样的错误。

我即将放弃并改为创建一个存储过程，但我无法理解为什么会发生超时。

Answer 1

当通过应用程序运行相同的查询时，SQL Server 正在使用的查询执行计划可能不同。检查您的执行计划。您可以在查询末尾使用 option(recompile) 之类的提示，或者如果对于不同的 id，返回的行显着不同，则可以针对特定的 Lineid 对其进行优化。 有时，使用此类提示会使其在 SSMS 中变慢，但在应用程序中却不会。经过一番尝试和尝试，您可以找到解决方案。