如何执行SQL“存在的地方"?在LINQ to Entities中? [英] How to do a SQL "Where Exists" in LINQ to Entities?

问题描述

我真的很想做这样的事情:

I really want to do something like this:

Select * 
from A join B on A.key = B.key join C on B.key = C.key -- propagated keys
where exists (select null from B where A.key = B.key and B.Name = "Joe") and
      exists (select null from C where B.key = C.key and C.Name = "Kim")

使用Entity Framework 4和C#时linq语句会是什么样?

What would the linq statement look like using Entity Framework 4 and C#?

更新:

显然.Contains()将产生"Where Exists"结果.因此，另一种尝试
(我不知道这是否还会编译大声笑):

Apparently .Contains() will produce "Where Exists" results. So, another attempt
(I don't know if this will even compile LOL):

var inner1 = from recordB in B
             where recordB.Name = "Joe"
             select recordB.key;

var inner2 = from recordC in C
             where recordC.Name = "Kim"
             select recordC.key;

var result = from recordA in A
             where inner1.Contains( recordA.key) &&
                   inner2.Contains( recordA.key)
             select recordA;

哇，这实际上是有效的:

WOW this is what actually worked:

var result = from A in Products
             where A.kfield1 == 1 && A.kfield2 == 2 &&
                   ( from B in Btable
                     where B.otherid == "Joe" &&  // field I want to select by
                           B.kfield1 == A.kfield1 &&     
                           B.kfield2 == A.kfield2 // Can keep adding keys here
                     select A.identifier  // unique identity field 
                   ).Contains(A.identifier) &&
                   ( from C in Ctable
                     where C.otherid == "Kim" &&  // field I want to select by
                           C.kfield1 == A.kfield1 &&     
                           C.kfield2 == A.kfield2 // Can keep adding keys here
                     select A.identifier  // unique identity field 
                   ).Contains(A.identifier)
             select A;

这产生了这个SQL:

SELECT [t0].[identifier], [t0].*
FROM [A] AS [t0]
WHERE ([t0].[kfield1] = @p0) AND ([t0].[kfield2] = @p1) AND (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [B] AS [t1]
    WHERE ([t0].[identifier] = [t0].[identifier]) AND ([t1].[otherid] = @p2) AND
          ([t1].[kfield1] = [t0].[kfield1]) AND 
          ([t1].[kfield2] = [t0].[kfield2]))) AND (EXISTS(
    SELECT NULL AS [EMPTY]
    FROM [C] AS [t2]
    WHERE ([t0].[identifier] = [t0].[identifier]) AND ([t2].[otherid] = @p3) AND
          ([t2].[kfield1] = [t0].[kfield1]) AND 
          ([t2].[kfiekd2] = [t0].[kfield2]) ))

我想要的是哪个.请注意[t0].[identifier] = [t0].[identifier]，它会滤除null值，因为null在SQL中不等于包括自身在内的所有值

Which is what I wanted. Notice the [t0].[identifier] = [t0].[identifier], which filters out null values because null doesn't compare equal to anything including itself (in SQL)

推荐答案

.Any()扩展方法通常映射到exists.

The .Any() extension method typically maps to exists.

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