SQL 如何使用 LAMBDA 表达式在 LINQ 中执行 IN 或 CONTAINS？
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How do you do an IN or CONTAINS in LINQ using LAMBDA expressions?
提问by mattruma
I have the following Transact-Sql that I am trying to convert to LINQ ... and struggling.
我有以下 Transact-Sql，我正在尝试将其转换为 LINQ ......并且正在挣扎。
SELECT * FROM Project
WHERE Project.ProjectId IN (SELECT ProjectId FROM ProjectMember Where MemberId = 'a45bd16d-9be0-421b-b5bf-143d334c8155')
Any help would be greatly appreciated ... I would like to do it with Lambda expressions, if possible.
任何帮助将不胜感激......如果可能的话，我想用 Lambda 表达式来做。
Thanks in advance!
提前致谢！
采纳答案by Strelok
GFrizzle beat me to it. But here is a C# version
GFrizzle 击败了我。但这里有一个 C# 版本
var projectsMemberWorkedOn = from p in Projects
join projectMember in ProjectMembers on
p.ProjectId equals projectMember.ProjectId
where projectMember.MemberId == "a45bd16d-9be0-421b-b5bf-143d334c8155"
select p;
And as a bonus a purely LINQ method chain version as well:
作为奖励，还有一个纯粹的 LINQ 方法链版本：
var projectsMemberWorkedOn =
Projects.Join( ProjectMembers, p => p.ProjectId, projectMember => projectMember.ProjectId,
( p, projectMember ) => new { p, projectMember } )
.Where( @t => @t.projectMember.MemberId == "a45bd16d-9be0-421b-b5bf-143d334c8155" )
.Select(@t => @t.p );
回答by Dave Markle
In this context, you can just use .Contains(), something like this:
在这种情况下，您可以只使用 .Contains()，如下所示：
var projects =
from p in db.Projects
where db.ProjectMembers.Where(m => m.MemberId == "a45bd16d-9be0-421b-b5bf-143d334c8155").Select(pp => pp.ProjectID).Contains(p.ProjectID)
select p;
回答by gfrizzle
No need for a lambda, you've just got a simple LINQ join here:
不需要 lambda，您只需在此处进行简单的 LINQ 连接：
From p in db.Projects _
Join m in db.ProjectMember On p.ProjectId Equals m.ProjectId _
Where m.MemberId = "a45bd16d-9be0-421b-b5bf-143d334c8155" _
Select p
回答by Mark Cidade
You probably want the Any()operator:
您可能需要Any()运算符：
var q = db.Projects
.Where(p => db.ProjectMembers
.Where(pm => pm.MemberId == memberId)
.Any (pm => p.ProjectId == pm.ProjectId));
Since the result set of db.ProjectMembers.Where(...)will always be the same, you can split it up so that it's executed only once:
由于结果集db.ProjectMembers.Where(...)总是相同的，您可以将其拆分，以便只执行一次：
var projectMembers = db.ProjectMembers.Where(pm => pm.MemberId == memberId);
var q = db.Projects
.Where(p => projectMembers
.Any(pm => p.ProjectId == pm.ProjectId));
