为什么 EF 6.4 生成的 SQL 出错了？答案

【问题标题】：Why is the EF 6.4 generated SQL faulty?为什么 EF 6.4 生成的 SQL 出错了？
【发布时间】：2021-08-19 23:27:14
【问题描述】：

我有一个看起来像这样的查询。 UserId 是随机字母字符串。 searchCritera 是要搜索的模型。 searchCriteria.MainRoleValueList 包含要搜索的角色（枚举）

var criteria = DBContext.People.Include(w => w.Main).AsQueryable();

//A lot of code that doesnt affect this senario.

if (!string.IsNullOrEmpty(searchCriteria.UserIdLike))
{
     criteria = criteria.Where(i => i.UserId.Contains(searchCriteria.UserIdLike));
}
if (searchCriteria.MainRoleValueList != null && searchCriteria.MainRoleValueList.Count > 0)
{
         var MainMembership = DBContext.MainMemberships.Where(p => searchCriteria.MainRoleValueList.Contains(p.MainRoleValue) && p.ValidTo == null).Join(criteria,
                        main => new { main.UserId, main.Main_Id }, current => new { current.UserId, current.Main_Id }, (main, current) => main);

var tmp = MainMembership.ToList(); //Added line to trigger communication with SQL server
}

生成的sql代码是

SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[UserId] AS [UserId], 
    [Extent1].[Main_Id] AS [Main_Id], 
    [Extent1].[MainRoleValue] AS [MainRoleValue], 
    [Extent1].[ValidFrom] AS [ValidFrom], 
    [Extent1].[ValidTo] AS [ValidTo]
    FROM  [dbo].[MainRoleMembership] AS [Extent1]
    INNER JOIN [dbo].[Person] AS [Extent2] ON ([Extent1].[UserId] = [Extent2].[UserId]) AND ([Extent1].[Main_Id] = [Extent2].[Main_Id])
    WHERE ([Extent1].[MainRoleValue] IN (300, 400, 200, 410)) AND ([Extent1].[ValidTo] IS NULL) AND (([Extent2].[FullName] LIKE '%rty12tt%' ESCAPE N'~') 
    OR ([Extent2].[UserId] LIKE '%rty12tt%' ESCAPE N'~')) AND 
    ( EXISTS (SELECT 
        1 AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
        WHERE 1 = 0
    ))

除了最后一部分，它还有效

EXISTS (SELECT 
        1 AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
        WHERE 1 = 0

为什么要添加这个？因为它删除了我想要的正确结果。如果我删除该部分并在 SQL 服务器上运行查询，我会得到我想要的用户。我应该如何重写我的查询以便不包括在内？

添加：是的，有 UserId 的两个表没有外键用户身份。这是系统中的一个糟糕设计，但我暂时无法修复。

添加：在表之间为 UserId 添加了一个外键，但没有帮助

【问题讨论】：

据我所知，这确实来自您认为的“大量代码不会影响此情景”。当 EF6 从模型约束 + 谓词推断谓词只能为假时，它总是这样做。
你在哪里对..有一个空列表，当它应该加入时添加

标签： sql entity-framework linq-to-entities

【解决方案1】：

我添加并与一个空列表进行比较..这就是为什么

EXISTS (SELECT 
        1 AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
        WHERE 1 = 0

已添加。为列表添加了计数检查，问题消失了

【讨论】：