Question

LINQ确实让我发疯！我已经使用了很多年了，但是仍然发现使用连接将SQL Server查询放在一起需要5分钟，而在LINQ中做同样的事情要花半天。

以下查询应采用一个productVersion并检索下游productTOC字段，然后将它们与userProduct表中的一组单独结果组合，该结果显示每个{{1 }}。 productTOC和userProduct之间没有直接链接，因为它们之间存在版本控制层，但我设法通过从productTOC up 到productTOC，然后从下到product，如果有记录，则检索该记录。但是，当我运行查询时，每个userProducts

会收到多个SQL查询
productTOC

例如：

发生的第一个查询是我所期望的：

private static IEnumerable<CompositeTocDataItem> GetCompositeTocData(P42Entities ctx, int userID, RSPlatform.Data.Core.ProductVersion productVersion) { return from toc in productVersion.ProductTOCs orderby toc.Position let up = toc.ReferenceProduct?.UserProducts.Where(UP=>UP.UserID == userID).FirstOrDefault() select new CompositeTocDataItem() { Position = toc.Position, Level = toc.Level, Name = toc.Name, ReferenceProductID = toc.ReferenceProductID, RefCode = toc.RefCode, ConditionInfo = toc.ConditionInfo, LastCompletedDate = up?.LastCompletedDate, Score = up?.Score, ScoreStatus = up?.ScoreStatus ?? "N", }; }

，但是对于每个 exec sp_executesql N'SELECT [Extent1].[ProductVersionID] AS [ProductVersionID], [Extent1].[Position] AS [Position], [Extent1].[Level] AS [Level], [Extent1].[Name] AS [Name], [Extent1].[RefCode] AS [RefCode], [Extent1].[ReferenceProductID] AS [ReferenceProductID], [Extent1].[ConditionInfo] AS [ConditionInfo] FROM [dbo].[ProductTOC] AS [Extent1] WHERE [Extent1].[ProductVersionID] = @EntityKeyValue1',N'@EntityKeyValue1 int',@EntityKeyValue1=177，有两个单独的查询，如下所示：

productTOC

和

exec sp_executesql N'SELECT [Extent1].[ID] AS [ID], ... [Extent1].[ProductCode] AS [ProductCode] FROM [dbo].[Product] AS [Extent1] WHERE [Extent1].[ID] = @EntityKeyValue1',N'@EntityKeyValue1 int',@EntityKeyValue1=79

如果我在SQL中执行此操作，则只需连接表并在单个查询中检索所需的内容。谁能告诉我为什么我要进行很多小的查找？谢谢。

Answer 1

如果您只是尝试将查询置于其他查询之外怎么办？喜欢

private static IEnumerable<CompositeTocDataItem> GetCompositeTocData(P42Entities ctx, int userID, RSPlatform.Data.Core.ProductVersion productVersion)
    {
 var up = productVersion.ProductTOCs.ReferenceProduct?.UserProducts.Where(UP=>UP.UserID == userID).FirstOrDefault(); //do it HERE ..so it hit the DB only once..and then you work in memory

        return from toc in productVersion.ProductTOCs
               orderby toc.Position

               select new CompositeTocDataItem()
               {
                   Position = toc.Position,
                   Level = toc.Level,
                   Name = toc.Name,

                   ReferenceProductID = toc.ReferenceProductID,
                   RefCode = toc.RefCode,
                   ConditionInfo = toc.ConditionInfo,
                   LastCompletedDate = up?.LastCompletedDate,
                   Score = up?.Score,
                   ScoreStatus = up?.ScoreStatus ?? "N",
               };
    }

希望它对您有帮助

使用linq查询SQL Server导致100多个小查询

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