我想了解如何使用“包含”而不是“等于”來加入兩個串列。SO上有類似的問題，但似乎沒有任何效果。這是我的示例代碼，我的目的是讓不屬于任何教室的學生：
var a = new Student("A");
var b = new Student("B");
var c = new Student("C");
var d = new Student("D");
var e = new Student("E");
var f = new Student("F");
var students = new List<Student>() { a, b, c, d, e, f };
var classRoomA = new ClassRoom();
classRoomA.Students.Add(a);
classRoomA.Students.Add(b);
var classRoomB = new ClassRoom();
classRoomB.Students.Add(c);
classRoomB.Students.Add(d);
var classRoomC = new ClassRoom();
classRoomC.Students.Add(e);
var classes = new List<ClassRoom> { classRoomA, classRoomB, classRoomC };
//option A. This works
var studentsWithoutClassRoom = students
.Where(stu => !classes.Any(r => r.Students.Contains(stu)))
.Select(s => s);
//optionB .This in one of many options that
//I have tried and it gives very interesting results
var studentsWithoutClassRoomTest = from w in students
from l in classes
where !l.Students.Contains(w)
select l;
如您所見，我可以使用 optionA 得到答案，但我想了解是否可以使用 optionB 中的方法完成它？
uj5u.com熱心網友回復：
嘗試以下查詢：
var studentsWithoutClassRoomTest =
from w in students
join s in classes.SelectMany(c => c.Students) on w equals s into gj
from s in gj.DefaultIfEmpty()
where s == null
select w;
uj5u.com熱心網友回復：
當您的目標是找到不屬于的人（與加入相反）時，我認為我不會說您正在“加入”兩個串列。
因此，我將創建 aHashSet中的所有Students，ClassRoom然后找到Student不在該集合中的 s：
var studentsWithClassRooms = (from cr in classRooms
from s in cr.Students
select s).ToHashSet();
var studentsWithoutClassRoomTest = from s in students
where !studentsWithClassRooms.Contains(s)
select s;
我認為加入 byContains更像是生成一個Students 串列和ClassRoom它們所屬的 s （假設 aStudent可能在多個中ClassRoom）：
var studentsAndClassRooms = from s in students
from cr in classRooms
where cr.Students.Contains(s)
group cr by s into crg
select new { s = crg.Key, crg };
uj5u.com熱心網友回復：
var studentsWithoutClassRoomTest = from w in students
from l in classes
where !l.Students.Contains(w)
select l;
如果你想要學生，你不應該選擇w而不是選擇嗎？l
使用join代替from并給出加入條件on
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標籤：C＃林克
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