Question

我们有一个相当简单的表，我们试图用Entity Framework查询，看起来像这样：

CREATE TABLE [dbo].[EFBlkFireRisks](
    [EFBlkFireRiskId] [int] IDENTITY(1,1) NOT NULL,
    [EFStateId] [int] NOT NULL,
    [Lat] [decimal](18, 8) NOT NULL,
    [Lon] [decimal](18, 8) NOT NULL,
    [AdjustedPremiumMultiplier] [decimal](18, 4) NOT NULL DEFAULT ((0)),
    [GeoLocation] [geography] NULL,
 CONSTRAINT [PK_dbo.EFBlkFireRisks] PRIMARY KEY CLUSTERED 
(
    [EFBlkFireRiskId] ASC
)

它在GeoLocation列上有一个地理空间索引，如下所示：

CREATE SPATIAL INDEX [IX_EFBlkFireRisks_Spatial] ON [dbo].[EFBlkFireRisks]
(
    [GeoLocation]
)USING  GEOGRAPHY_AUTO_GRID

我们试图在该表中找到最接近给定纬度/经度点的条目。

C＃查询如下所示：

var geoPoint = SqlSchemaFunctions.GetDbGeography(lat, lon);
var query = ctx.BulkFireRisks
    .Where(x => x.EFStateId == stateId && x.GeoLocation.Distance(geoPoint) != null)
    .OrderBy(x => x.GeoLocation.Distance(geoPoint));
var bfr = query.First();

查询生成的SQL看起来基本上是这样的：

declare @p3 sys.geography set @p3=convert(sys.geography,0xE6100000010C8FC2F5285CFF434052B81E85EB515AC0)
declare @p4 sys.geography set @p4=convert(sys.geography,0xE6100000010C8FC2F5285CFF434052B81E85EB515AC0)
exec sp_executesql N'SELECT TOP (1) 
    [Project1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
    [Project1].[EFStateId] AS [EFStateId], 
    [Project1].[GeoId] AS [GeoId], 
    [Project1].[Lat] AS [Lat], 
    [Project1].[Lon] AS [Lon], 
    [Project1].[GeoLocation] AS [GeoLocation], 
    [Project1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier],
    [Project1].C1 as Distance
    FROM ( SELECT 
        [Extent1].[GeoLocation].STDistance(@p__linq__1) AS [C1], 
        [Extent1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
        [Extent1].[EFStateId] AS [EFStateId], 
        [Extent1].[GeoId] AS [GeoId], 
        [Extent1].[Lat] AS [Lat], 
        [Extent1].[Lon] AS [Lon], 
        [Extent1].[GeoLocation] AS [GeoLocation], 
        [Extent1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier]
        FROM [dbo].[EFBlkFireRisks] AS [Extent1]
        WHERE (11 = [Extent1].[EFStateId]) AND ([Extent1].[GeoLocation].STDistance(@p__linq__0) IS NOT NULL)
    )  AS [Project1]
    ORDER BY [Project1].[C1] ASC',N'@p__linq__0 [geography],@p__linq__1 [geography]',@p__linq__0=@p3,@p__linq__1=@p4

该查询不使用索引 - 将其置于循环中并运行10次大约需要30秒（无论是通过SQL手动执行，还是通过C＃从EF运行）

但是，可以删除sp_executesql位，并直接运行查询，如下所示：

declare @p3 sys.geography set @p3=convert(sys.geography,0xE6100000010C8FC2F5285CFF434052B81E85EB515AC0)
SELECT TOP (1) 
    [Project1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
    [Project1].[EFStateId] AS [EFStateId], 
    [Project1].[GeoId] AS [GeoId], 
    [Project1].[Lat] AS [Lat], 
    [Project1].[Lon] AS [Lon], 
    [Project1].[GeoLocation] AS [GeoLocation], 
    [Project1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier],
    [Project1].C1 as Distance
    FROM ( SELECT 
        [Extent1].[GeoLocation].STDistance(@p3) AS [C1], 
        [Extent1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
        [Extent1].[EFStateId] AS [EFStateId], 
        [Extent1].[GeoId] AS [GeoId], 
        [Extent1].[Lat] AS [Lat], 
        [Extent1].[Lon] AS [Lon], 
        [Extent1].[GeoLocation] AS [GeoLocation], 
        [Extent1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier]
        FROM [dbo].[EFBlkFireRisks] AS [Extent1]
        WHERE (11 = [Extent1].[EFStateId]) AND ([Extent1].[GeoLocation].STDistance(@p3) IS NOT NULL)
    )  AS [Project1]
    ORDER BY [Project1].[C1] asc

并且查询不会运行30 秒，但是30 毫秒。

我在挠头。知道两个查询为什么有这么截然不同的执行模式？知道如何让EF使用这个特定的地理空间索引吗？我做错了什么？

编辑6/18 - 如果我尝试向较慢的sp_executesql查询添加索引提示，则会收到以下错误消息：

查询处理器无法为具有空间索引提示的查询生成查询计划。原因：空间索引不支持谓词中提供的比较器。

相同的提示在另一个查询中起作用 - 或者至少不会出错 -

慢速查询的查询计划如下所示：

Geospatial Query Plan

换句话说，它没有拿起地理空间索引。快速版的查询计划是获取索引，看起来像您期望的那样：

enter image description here

这是在SQL Server 2014上运行的：

（Microsoft SQL Server 2014 - 12.0.2000.8（X64） 2014年2月20日20:04:26 版权所有（c）Microsoft Corporation Windows NT 6.3（Build 9600：）
上的Express Edition（64位）

Answer 1

好的，我明白了。

事实证明，这两个查询并不完全相同：sp_executesql版本有两个参数，而快速版只有一个参数：这就是关键。这个查询（只有一个参数）就像你期望的那样执行：

declare @p3 sys.geography
set @p3=convert(sys.geography,0xE6100000010C8FC2F5285CFF434052B81E85EB515AC0)
exec sp_executesql N'SELECT TOP (1) 
    [Project1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
    [Project1].[EFStateId] AS [EFStateId], 
    [Project1].[GeoId] AS [GeoId], 
    [Project1].[Lat] AS [Lat], 
    [Project1].[Lon] AS [Lon], 
    [Project1].[GeoLocation] AS [GeoLocation], 
    [Project1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier]
    FROM ( SELECT 
        [Extent1].[EFBlkFireRiskId] AS [EFBlkFireRiskId], 
        [Extent1].[EFStateId] AS [EFStateId], 
        [Extent1].[GeoId] AS [GeoId], 
        [Extent1].[Lat] AS [Lat], 
        [Extent1].[Lon] AS [Lon], 
        [Extent1].[GeoLocation] AS [GeoLocation], 
        [Extent1].[AdjustedPremiumMultiplier] AS [AdjustedPremiumMultiplier], 
        [Extent1].[GeoLocation].STDistance(@p__linq__0) AS [C1]
        FROM [dbo].[EFBlkFireRisks] AS [Extent1]
        WHERE (11 = [Extent1].[EFStateId]) AND ([Extent1].[GeoLocation].STDistance(@p__linq__0) IS NOT NULL)
    )  AS [Project1]
    ORDER BY [Project1].[C1] ASC',N'@p__linq__0 [geography]',@p__linq__0=@p3

在LINQ中获取该查询的方法如下：

var geoPoint = DbGeography.PointFromText(string.Format("POINT({0} {1})", lon, lat), 4326);
var q2 = (from b in ctx.BulkFireRisks
          let distance = b.GeoLocation.Distance(geoPoint)
          where b.EFStateId == stateId && distance != null
          orderby distance
          select b);
var bfr = q2.First();

关键是只定义一次sys.geography变量。

让实体框架与SQL Server地理空间索引一起使用

1 个答案: