查询Linq到Sql Entity Framework C＃

Question

我在SQL中有此查询，但是我不知道如何在Linq中进行查询

这是查询

SELECT 
    GroupName, GroupsId 
FROM 
    Groups 
WHERE 
    GroupsId NOT IN (SELECT Groups.GroupsId 
                     FROM AssignGroups 
                     JOIN Groups ON AssignGroups.GroupsId = Groups.GroupsID 
                                 AND AssignGroups.UsersId = 1) 
ORDER BY 
    GroupName

我正在使用EF。

Answer 1

var result = from group in Groups
             let validGroups = from aGroup in AssignGroups 
                               from vGroup in Groups 
                               where aGroup.GroupsId == vGroup.GroupsID  &&
                               vGroup.UserId == 1
                               select vGroup.GroupsID
             where validGroups.Contains(group.GroupID)
             orderby group.GroupName
             select group;

此处的关键是创建子查询的“ let”子句，它是IQueryable <T>，因此可以与“ Contains”子句一起使用（最后将其翻译为“ IN（）”子句）。

Answer 2

1）您可以优化查询：

SELECT
  g.GroupName
, g.GroupsId
FROM Groups g
LEFT JOIN AssignGroups ag
       ON g.GroupsId = ag.GroupsId
      AND ag.UsersId = 1
WHERE ag.GroupsId IS NULL
ORDER BY g.GroupName

2）您的linq查询：

from g in context.Groups
join ag in context.AssignGroups
on new {g.GroupsId, UsersId = 1} equals new {ag.GroupsId, ag.UsersId} into ags
from ag in ags.DefaultIfEmpty()
where ag.GroupsId == null
orderby g.GroupName
select new {g.GroupName, g.GroupsId}