LINQ中的關係部門？

Question

關係部門是Codd的原始關係運算符之一，通俗地說，它是供應所有零件的供應商。已經有各種翻譯成SQL的例子Celko使用the pilots who can fly all the planes in the hangar的例子討論了幾種方法。

我更喜歡的是「與集合操作員的分工」，因爲它是「剩餘的」（即威爾遜也可以飛F-17戰鬥機，但機庫中沒有一個）以及它如何處理案件除數是空集（即當機庫是空的，那麼所有的飛行員返回）：

WITH PilotSkills 
    AS 
    (
     SELECT * 
     FROM (
       VALUES ('Celko', 'Piper Cub'), 
        ('Higgins', 'B-52 Bomber'), ('Higgins', 'F-14 Fighter'), 
        ('Higgins', 'Piper Cub'), 
        ('Jones', 'B-52 Bomber'), ('Jones', 'F-14 Fighter'), 
        ('Smith', 'B-1 Bomber'), ('Smith', 'B-52 Bomber'), 
        ('Smith', 'F-14 Fighter'), 
        ('Wilson', 'B-1 Bomber'), ('Wilson', 'B-52 Bomber'), 
        ('Wilson', 'F-14 Fighter'), ('Wilson', 'F-17 Fighter') 
      ) AS T (pilot_name, plane_name) 
    ), 
    Hangar 
    AS 
    (
     SELECT * 
     FROM (
       VALUES ('B-1 Bomber'), 
        ('B-52 Bomber'), 
        ('F-14 Fighter') 
      ) AS T (plane_name) 
    ) 
SELECT DISTINCT pilot_name 
    FROM PilotSkills AS P1 
WHERE NOT EXISTS (
        SELECT plane_name 
        FROM Hangar 
        EXCEPT 
        SELECT plane_name 
        FROM PilotSkills AS P2 
        WHERE P1.pilot_name = P2.pilot_name 
       ); 

現在我需要在LINQ這樣做是爲了對象。這裏有一個建議直接翻譯：

var hangar = new [] 
{ 
    new { PlaneName = "B-1 Bomber" }, 
    new { PlaneName = "F-14 Fighter" }, 
    new { PlaneName = "B-52 Bomber" } 
}.AsEnumerable(); 

var pilotSkills = new [] 
{ 
    new { PilotName = "Celko", PlaneName = "Piper Cub" }, 
    new { PilotName = "Higgins", PlaneName = "B-52 Bomber" }, 
    new { PilotName = "Higgins", PlaneName = "F-14 Fighter" }, 
    new { PilotName = "Higgins", PlaneName = "Piper Cub" }, 
    new { PilotName = "Jones", PlaneName = "B-52 Bomber" }, 
    new { PilotName = "Jones", PlaneName = "F-14 Fighter" }, 
    new { PilotName = "Smith", PlaneName = "B-1 Bomber" }, 
    new { PilotName = "Smith", PlaneName = "B-52 Bomber" }, 
    new { PilotName = "Smith", PlaneName = "F-14 Fighter" }, 
    new { PilotName = "Wilson", PlaneName = "B-1 Bomber" }, 
    new { PilotName = "Wilson", PlaneName = "B-52 Bomber" }, 
    new { PilotName = "Wilson", PlaneName = "F-14 Fighter" }, 
    new { PilotName = "Wilson", PlaneName = "F-17 Fighter" } 
}.AsEnumerable(); 

var actual = pilotSkills.Where 
(
    p1 => hangar.Except 
    ( 
     pilotSkills.Where(p2 => p2.PilotName == p1.PilotName) 
        .Select(p2 => new { p2.PlaneName }) 
    ).Any() == false 
).Select(p1 => new { p1.PilotName }).Distinct(); 

var expected = new [] 
{ 
    new { PilotName = "Smith" }, 
    new { PilotName = "Wilson" } 
}; 

Assert.That(actual, Is.EquivalentTo(expected)); 

由於LINQ is supposedly based on the relational algebra然後直接翻譯似乎是合理的。但是有沒有更好的「原生」LINQ方法？

---

反思@Daniel Hilgarth的回答，在.NET土地的數據很可能是「組合」以開始：

var pilotSkills = new [] 
{ 
    new { PilotName = "Celko", 
      Planes = new [] 
      { new { PlaneName = "Piper Cub" }, } }, 
    new { PilotName = "Higgins", 
      Planes = new [] 
      { new { PlaneName = "B-52 Bomber" }, 
       new { PlaneName = "F-14 Fighter" }, 
       new { PlaneName = "Piper Cub" }, } }, 
    new { PilotName = "Jones", 
      Planes = new [] 
      { new { PlaneName = "B-52 Bomber" }, 
       new { PlaneName = "F-14 Fighter" }, } }, 
    new { PilotName = "Smith", 
      Planes = new [] 
      { new { PlaneName = "B-1 Bomber" }, 
       new { PlaneName = "B-52 Bomber" }, 
       new { PlaneName = "F-14 Fighter" }, } }, 
    new { PilotName = "Wilson", 
      Planes = new [] 
      { new { PlaneName = "B-1 Bomber" }, 
       new { PlaneName = "B-52 Bomber" }, 
       new { PlaneName = "F-14 Fighter" }, 
       new { PlaneName = "F-17 Fighter" }, } }, 
}; 

...和預測只是名稱是任意的，使得可能的解決方案要簡單得多：

// Easy to understand at a glance: 
var actual1 = pilotSkills.Where(x => hangar.All(y => x.Planes.Contains(y))); 

// Potentially more efficient: 
var actual = pilotSkills.Where(x => !hangar.Except(x.Planes).Any()); 

Answer 1

下應產生相同的結果：

pilotSkills.GroupBy(x => x.PilotName, x => x.PlaneName) 
      .Where(g => hangar.All(y => g.Contains(y.PlaneName))) 

這將返回一個組，每個飛行員可以飛機庫中的所有飛機。
該組的關鍵是飛行員的名字，該組的內容是飛行員可以飛行的所有飛機，即使是那些不在機庫的飛機。

如果您現在只想要飛行員，您可以在查詢的末尾添加一個.Select(g => new { PilotName = g.Key })。

---

使用上述方法與Except，使其更接近OP的原文：

pilotSkills.GroupBy(x => x.PilotName, x => new { x.PlaneName }) 
      .Where(g => !hangar.Except(g).Any()); 

這第二個查詢可能更好，因爲它遍歷g只有一次;用Contains的第一個查詢重複N次，其中N是機庫中的飛機數量。

Answer 2

使用@Daniel Hilgarth的答案，但這種方法更接近我的原文：

var actual = pilotSkills 
       .GroupBy(x => x.PilotName, x => new { x.PlaneName }) 
       .Where(g => !hangar.Except(g).Any()) 
       .Select(x => new { PilotName = x.Key });