如何使用 LINQ to SQL 处理 IN 子查询？

Question

我对此有点困惑。基本上我想在 LINQ to SQL 中执行类似以下 SQL 查询的操作：

SELECT f.* 
FROM Foo f
WHERE f.FooId IN (
    SELECT fb.FooId
    FROM FooBar fb
    WHERE fb.BarId = 1000
)

任何帮助将不胜感激。

谢谢。

Answer 1

看一下 本文. 。基本上，如果你想获得 IN 的等价物，你需要先构造一个内部查询，然后使用 Contains() 方法。这是我的翻译尝试：

var innerQuery = from fb in FoorBar where fb.BarId = 1000 select fb.FooId;
var result = from f in Foo where innerQuery.Contains(f.FooId) select f;

Answer 2

在 LINQ to SQL 中实现 IN 的一般方法

var q = from t1 in table1
        let t2s = from t2 in table2
                  where <Conditions for table2>
                  select t2.KeyField
        where t2s.Contains(t1.KeyField)
        select t1;

在 LINQ to SQL 中实现 EXISTS 的一般方法

var q = from t1 in table1
        let t2s = from t2 in table2
                  where <Conditions for table2>
                  select t2.KeyField
        where t2s.Any(t1.KeyField)
        select t1;

Answer 3

from f in Foo
    where f.FooID ==
        (
            FROM fb in FooBar
            WHERE fb.BarID == 1000
            select fb.FooID

        )
    select f;

Answer 4

尝试使用两个单独的步骤：

// create a Dictionary / Set / Collection fids first
var fids = (from fb in FooBar
            where fb.BarID = 1000
            select new { fooID = fb.FooID, barID = fb.BarID })
            .ToDictionary(x => x.fooID, x => x.barID);

from f in Foo
where fids.HasKey(f.FooId)
select f

Answer 5

// 首先创建一个字典/集合/集合fids

查找其他文章

var fids = (from fb in FooBar
            where fb.BarID = 1000
            select new { fooID = fb.FooID, barID = fb.BarID })
            .ToDictionary(x => x.fooID, x => x.barID);

from f in Foo
where fids.HasKey(f.FooId)
select f

Answer 6

尝试这个

var fooids = from fb in foobar where fb.BarId=1000 select fb.fooID
var ff = from f in foo where f.FooID = fooids select f

Answer 7

var foos = Foo.Where<br>
( f => FooBar.Where(fb.BarId == 1000).Select(fb => fb.FooId).Contains(f.FooId));

Answer 8

from f in foo
where f.FooID equals model.FooBar.SingleOrDefault(fBar => fBar.barID = 1000).FooID
select new
{
f.Columns
};

Answer 9

// 首先创建一个字典/集合/集合fids

查找其他文章

var fids = (from fb in FooBar where fb.BarID = 1000 select new { fooID = fb.FooID, barID = fb.BarID }) .ToDictionary(x => x.fooID, x => x.barID);

from f in Foo where fids.HasKey(f.FooId) select f