Question

这是我想要的查询：

select top 10 *
from vw_BoosterTargetLog
where OrganizationId = 4125
order by Id desc

它执行亚秒。

这是我的实体框架（6.1.2）在C＃中的等价物：

return await db.vw_BoosterTargetLog
    .Where(x => x.OrganizationId == organizationId)
    .OrderByDescending(x => x.Id)
    .Take(numberToRun)
    .ToListNolockAsync();

这是它生成的SQL：

SELECT TOP (10) 
    [Project1].[OrganizationId] AS [OrganizationId], 
    [Project1].[BoosterTriggerId] AS [BoosterTriggerId], 
    [Project1].[IsAutomatic] AS [IsAutomatic], 
    [Project1].[C1] AS [C1], 
    [Project1].[CustomerUserId] AS [CustomerUserId], 
    [Project1].[SourceUrl] AS [SourceUrl], 
    [Project1].[TargetUrl] AS [TargetUrl], 
    [Project1].[ShowedOn] AS [ShowedOn], 
    [Project1].[ClickedOn] AS [ClickedOn], 
    [Project1].[BoosterTargetId] AS [BoosterTargetId], 
    [Project1].[TriggerEventGroup] AS [TriggerEventGroup], 
    [Project1].[TriggerIgnoreIdentifiedUsers] AS [TriggerIgnoreIdentifiedUsers], 
    [Project1].[TargetTitle] AS [TargetTitle], 
    [Project1].[BoosterTargetVersionId] AS [BoosterTargetVersionId], 
    [Project1].[Version] AS [Version], 
    [Project1].[CookieId] AS [CookieId], 
    [Project1].[CoalescedId] AS [CoalescedId], 
    [Project1].[OrganizationName] AS [OrganizationName], 
    [Project1].[ShowedOnDate] AS [ShowedOnDate], 
    [Project1].[SampleGroupSectionName] AS [SampleGroupSectionName], 
    [Project1].[Selector] AS [Selector], 
    [Project1].[SelectorStep] AS [SelectorStep]
    FROM ( SELECT 
        [Extent1].[OrganizationId] AS [OrganizationId], 
        [Extent1].[OrganizationName] AS [OrganizationName], 
        [Extent1].[BoosterTriggerId] AS [BoosterTriggerId], 
        [Extent1].[IsAutomatic] AS [IsAutomatic], 
        [Extent1].[SampleGroupSectionName] AS [SampleGroupSectionName], 
        [Extent1].[Selector] AS [Selector], 
        [Extent1].[SelectorStep] AS [SelectorStep], 
        [Extent1].[BoosterTargetId] AS [BoosterTargetId], 
        [Extent1].[CookieId] AS [CookieId], 
        [Extent1].[CustomerUserId] AS [CustomerUserId], 
        [Extent1].[CoalescedId] AS [CoalescedId], 
        [Extent1].[SourceUrl] AS [SourceUrl], 
        [Extent1].[TriggerEventGroup] AS [TriggerEventGroup], 
        [Extent1].[TriggerIgnoreIdentifiedUsers] AS [TriggerIgnoreIdentifiedUsers], 
        [Extent1].[TargetTitle] AS [TargetTitle], 
        [Extent1].[TargetUrl] AS [TargetUrl], 
        [Extent1].[ShowedOn] AS [ShowedOn], 
        [Extent1].[ShowedOnDate] AS [ShowedOnDate], 
        [Extent1].[ClickedOn] AS [ClickedOn], 
        [Extent1].[BoosterTargetVersionId] AS [BoosterTargetVersionId], 
        [Extent1].[Version] AS [Version], 
         CAST( [Extent1].[Id] AS int) AS [C1]
        FROM (SELECT 
    [vw_BoosterTargetLog].[OrganizationId] AS [OrganizationId], 
    [vw_BoosterTargetLog].[OrganizationName] AS [OrganizationName], 
    [vw_BoosterTargetLog].[BoosterTriggerId] AS [BoosterTriggerId], 
    [vw_BoosterTargetLog].[IsAutomatic] AS [IsAutomatic], 
    [vw_BoosterTargetLog].[SampleGroupSectionName] AS [SampleGroupSectionName], 
    [vw_BoosterTargetLog].[Selector] AS [Selector], 
    [vw_BoosterTargetLog].[SelectorStep] AS [SelectorStep], 
    [vw_BoosterTargetLog].[BoosterTargetId] AS [BoosterTargetId], 
    [vw_BoosterTargetLog].[CookieId] AS [CookieId], 
    [vw_BoosterTargetLog].[CustomerUserId] AS [CustomerUserId], 
    [vw_BoosterTargetLog].[CoalescedId] AS [CoalescedId], 
    [vw_BoosterTargetLog].[Id] AS [Id], 
    [vw_BoosterTargetLog].[SourceUrl] AS [SourceUrl], 
    [vw_BoosterTargetLog].[TriggerEventGroup] AS [TriggerEventGroup], 
    [vw_BoosterTargetLog].[TriggerIgnoreIdentifiedUsers] AS [TriggerIgnoreIdentifiedUsers], 
    [vw_BoosterTargetLog].[TargetTitle] AS [TargetTitle], 
    [vw_BoosterTargetLog].[TargetUrl] AS [TargetUrl], 
    [vw_BoosterTargetLog].[ShowedOn] AS [ShowedOn], 
    [vw_BoosterTargetLog].[ShowedOnDate] AS [ShowedOnDate], 
    [vw_BoosterTargetLog].[ClickedOn] AS [ClickedOn], 
    [vw_BoosterTargetLog].[BoosterTargetVersionId] AS [BoosterTargetVersionId], 
    [vw_BoosterTargetLog].[Version] AS [Version]
    FROM [dbo].[vw_BoosterTargetLog] AS [vw_BoosterTargetLog]) AS [Extent1]
        WHERE [Extent1].[OrganizationId] = 4125
    )  AS [Project1]
    ORDER BY [Project1].[C1] DESC

当然，它很丑陋，因为所有的EF查询都是：我并没有抱怨这一点。我的抱怨是，在我的测试中，最好的情况是，它的执行速度比第一次慢10倍，而最坏的情况则慢约100倍。

对于一个简单的查询，这似乎超出了所有合理的期望。

显然我可以直接执行SQL，或执行一个sproc，或者那种类型的东西。虽然我在等待反馈，但这就是我要做的事情。但有没有人有任何其他建议如何加快速度？有没有办法鼓励EF在这样的情况下生成合理的SQL？

Answer 1

EF产生的查询虽然从可读性的角度来看很糟糕，但通常仍然非常合理 - 我说这是通过手写查询通过存储过程进行几乎所有数据访问的人。但是为了使它工作，模型EF需要数据库需要与实际数据库匹配，否则将引入转换，当发生这种情况时，非常很容易变得可怕在转换所有数据并且不能使用索引时性能下降。

如果我们消除了一些嵌套，EF查询可以简化为

SELECT TOP (10) *
FROM (
    SELECT *, CAST(Id AS INT) AS C1
    FROM vw_BoosterTargetLog
    WHERE OrganizationId = 4125
) _
ORDER BY C1 DESC

（这不是实际的结果集，因为Id不是真实查询中最终结果集的一部分，但假装我像EF一样写出了所有列。）

如果vw_BoosterTargetLog.Id实际上不是INT，则会在排序发生之前强制转换所有行，这会慢得多。解决方案是找出列的实际类型（在本例中为BIGINT）并相应地更新模型。

实体框架6生成的非常低效的查询

1 个答案: