带 EF Core 6.0 和 SQL 服务器的 GroupBy

Question

我有一个 Blazor Web 应用程序，它已经在现场工作了几个月。我想将数据库查询扩展到一组类似的“检测”。

它是从 .NET 5 开始编写的，就在今天更新到 .NET 6 试图让它工作。

我想知道如何获取按 TimeStamp（日期时间属性）排序的结果。我有一个内存数据库的工作示例，但生产将在 SQL 服务器中。我在 SQL 方面不是很好，但我在 Management Studio 中玩了一段时间但运气不好。

注释掉 OrderByDescending() 正确分组，但结果顺序不正确。似乎 EF 翻译过程完全删除了该行，它对生成的查询或结果集没有影响。

var results = context.Detections
//Line below makes no change ignored by SQL Server. Works when using in memory DB.
    //.OrderByDescending(det => det.TimeStamp) 
    .GroupBy(det => new
    {
        Year = det.TimeStamp.Year,
        Month = det.TimeStamp.Month,
        Day = det.TimeStamp.Day,
        Hour = det.TimeStamp.Hour,
    })
    .Select(grp => new
    {
        Count = grp.Count(),
        Detection = grp.OrderByDescending(det => det.TimeStamp).First(),
    })
//The following line will not translate
    //.OrderByDescending(det => det.Detection.TimeStamp)
    .ToList();

如果有任何问题：

Visual Studio 2022 (4.8.04084)
.Net 6.0
SQL 服务器 2019 (15.0.2080.9)
*所有与 EF 相关的 NuGet 包已更新至 6.0

编辑澄清
上面的代码段产生以下 SQL 查询。

SELECT [t].[c], [t0].[Id], [t0].[TimeStamp]
FROM (
    SELECT COUNT(*) AS [c], DATEPART(year, [d].[TimeStamp]) AS [c0], DATEPART(month, [d].[TimeStamp]) AS [c1], DATEPART(day, [d].[TimeStamp]) AS [c2], DATEPART(hour, [d].[TimeStamp]) AS [c3]
    FROM [Detections] AS [d]
    WHERE [d].[TimeStamp] > DATEADD(day, CAST(-16.0E0 AS int), GETUTCDATE())
    GROUP BY DATEPART(year, [d].[TimeStamp]), DATEPART(month, [d].[TimeStamp]), DATEPART(day, [d].[TimeStamp]), DATEPART(hour, [d].[TimeStamp])
) AS [t]
OUTER APPLY (
    SELECT TOP(1) [d0].[Id], [d0].[TimeStamp]
    FROM [Detections] AS [d0]
    WHERE ([d0].[TimeStamp] > DATEADD(day, CAST(-30.0E0 AS int), GETUTCDATE())) AND (((([t].[c0] = DATEPART(year, [d0].[TimeStamp])) AND ([t].[c1] = DATEPART(month, [d0].[TimeStamp]))) AND ([t].[c2] = DATEPART(day, [d0].[TimeStamp]))) AND ([t].[c3] = DATEPART(hour, [d0].[TimeStamp])))
    ORDER BY [d0].[TimeStamp] DESC
) AS [t0]

它产生类似于以下的结果。注意没有按时间排序。

1   628591  2021-11-02 14:34:06.0442966  
10  628601  2021-11-12 05:43:27.7015291  
150 628821  2021-11-12 21:59:27.6444236  
20  628621  2021-11-12 06:17:13.7798282  
50  628671  2021-11-12 15:17:23.8893856

如果我在 Management Studio 中的那个 SQL 查询的末尾添加 ORDER BY [t0].TimeStamp DESC，我会得到我正在寻找的结果（见下文）。我只需要知道如何在 LINQ 中编写它。

150 628821  2021-11-12 21:59:27.6444236  
50  628671  2021-11-12 15:17:23.8893856  
20  628621  2021-11-12 06:17:13.7798282  
10  628601  2021-11-12 05:43:27.7015291  
1   628591  2021-11-02 14:34:06.0442966

在 ToList() 之前的末尾添加 .OrderByDescending(det => det.Detection.TimeStamp) 是我的第一个想法，但“无法翻译”。我需要对这些结果进行分页，所以我真的很想在 SQL.

中进行排序

Answer 1

GroupBy 必须自己进行排序，这样 'ignores' 才不会完全出乎意料。

将其移至分组下方：

var results = context.Detections
    //.OrderByDescending(det => det.TimeStamp) 
    .GroupBy(det => new
    {
        Year = det.TimeStamp.Year,
        Month = det.TimeStamp.Month,
        Day = det.TimeStamp.Day,
        Hour = det.TimeStamp.Hour,
    })
//    .OrderByDescending(grp => grp.Key)  // may have to split into y/m/d/h again
    .OrderByDescending(grp => grp.Key.Year)
       .ThenByDescending( grp => grp.Key.Month)
       .ThenByDescending( grp => grp.Key.Day)
       .ThenByDescending( grp => grp.Key.Hour)
    .Select(grp => new
    {
        Count = grp.Count(),
        Detection = grp.OrderByDescending(det => det.TimeStamp).First(),
    })
    .ToList();

当 EF 支持时，

的排序和分组可能会变得更容易一些

.GroupBy(det => new
{
    Date = det.TimeStamp.Date,
    Hour = det.TimeStamp.Hour,
})

Answer 2

对于以后查看此内容的任何人。

我能够通过声明和填充 TimeStamp 属性并在末尾使用 OrderByDescending() 来完成这项工作。我不确定这是否是最佳解决方案，但它确实解决了我的问题。

var results = context.Detections
    .GroupBy(det => new
    {
        Year = det.TimeStamp.Year,
        Month = det.TimeStamp.Month,
        Day = det.TimeStamp.Day,
        Hour = det.TimeStamp.Hour,
    })
    .Select(grp => new
    {
        Count = grp.Count(),
        TimeStamp = grp.OrderByDescending(det => det.TimeStamp).First().TimeStamp,
        Detection = grp.OrderByDescending(det => det.TimeStamp).First(),
    })
    .OrderByDescending(det => det.TimeStamp)
    .ToList();

带 EF Core 6.0 和 SQL 服务器的 GroupBy

GroupBy with EF Core 6.0 and SQL Server

c#

sql-server

entity-framework

blazor

ef-core-6.0