Linq to SQL嵌套IN FROM查询

Question

任何人都可以告诉我如何编写嵌套的SQL查询,如

SELECT*FROM X WHERE X.ID IN(从Y WHERE中选择Y.XID .....)

在LINQ？

Answer 1

你可以尝试:

var yIds = from y in dataContext.Y
           where ...
           select y.XId;

var query = from x in dataContext.X
            where yIds.Contains(x.Id)
            select x;

我不知道它是否会起作用 - 你不想只是做一个连接的原因吗？例如:

var query = from x in dataContext.X
            join y in dataContext.Y.Where(...) on x.Id equals y.Xid
            select x;

Answer 2

要在sql中执行IN,您需要使用Linq中的Contains函数.

例如:

var query = from x in GetX()
            where (from y in GetY() select y.xID).Contains(x.xID)
            select x;

如果你愿意的话,你也可以单独定义内部linq查询,这样更具可读性

Answer 3

我一直在寻找NOT INLINQ to SQL 的解决方案.感谢这个问题,我能够google正确的事情并找到这篇博文:LINQ to SQL中的NOT IN子句

C#

NorthwindDataContext dc = new NorthwindDataContext();
var query =
    from c in dc.Customers
    where !(from o in dc.Orders
            select o.CustomerID)
           .Contains(c.CustomerID)
    select c;

VB.net

Dim db As New NorthwinDataContext()
Dim query = From c In dc.Customers _
            Where Not (From o in dc.Orders _
                       Select o.CustomerID).Contains(c.CustomerID) _
            Select c