Question

我正在尝试学习Linq，我需要一个方法来帮助查找List中的List，查找匹配项并删除它。例如，假设我有一个名为Student的类：

public class Student
{
   string FirstName;
   string LastName;
}

然后想象我有另一个名为Classroom的班级，其中有List<Student>：

public class Classroom
{
   List<Student> Students;
}

最后，我还有一个名为School的课程，其中有一个Classrooms列表：

public class School
{
   List<Classroom> Classrooms;
}

然后，我需要一个接收Student对象的方法，检查学生是否在学校，如果是，则删除它们。如果他们在学校，该方法应删除它们并返回true。如果他们不在学校，该方法应该返回false并且不采取任何行动。这是一个使用foreach循环的例子，我想摆脱它：

public bool RemoveStudentFromSchool(Student student)
{
   foreach (Classroom c in Classrooms)
   {
      foreach (Student s in c.Students)
      {
         if ((student.FirstName == s.FirstName) && (student.LastName == s.LastName))
         {
            s.Remove(student);

            return true;
         }
      }
   }

   return false;
}

Answer 1

这假设学生只能在一个房间，Student IEquatable姓名（或参考文献相同）：

var roomWithStudent = Classrooms.FirstOrDefault(c => c.Students.Any(s => s.Equals(student));
if (roomWithStudent != null)
{
    roomWithStudent.Remove(student);
    return true;
}
return false;

如果Student不是IEquatable并且传入的搜索对象不一定是同一个引用，那么另一种方法是：

var roomWithStudent = Classrooms
                        .SelectMany(c => c.Students.Select(s => new { Room = c, Student = s }))
                        .Where(rs => (student.FirstName == rs.Student.FirstName) && (student.LastName == rs.Student.LastName))
                        .FirstOrDefault();

if (roomWithStudent != null)
{
    roomWithStudent.Room.Students.Remove(roomWithStudent.Student);
    return true;
}
return false;

Answer 2

扩展方法怎么样..

public static bool RemoveFromRoom(this Student student,School school)
{
    if (student == null) throw new ArgumentNullException("student");
    if (school == null) throw new ArgumentNullException("school");
    bool ret = false;
    var room = school.Classrooms.SingleOrDefault(cr=>cr.Students.Contains(student));
    if (room !=null)
    {
        ret = true;
        room.Students.Remove(student);
    }

    return ret;
}

用法

student.RemoveFromRoom(instanceOfSchool);

或者...

public static bool RemoveStudentFromRoom(this School school,Student student)
{
    if (student == null) throw new ArgumentNullException("student");
    if (school == null) throw new ArgumentNullException("school");
    bool ret = false;
    var room = school.Classrooms.SingleOrDefault(cr=>cr.Students.Contains(student));
    if (room !=null)
    {
        ret = true;
        room.Students.Remove(student);
    }

    return ret;
}

用法

instanceOfSchool.RemoveStudentFromRoom(student);

Linq lambda用于搜索列表中的列表，查找匹配项，然后从列表中删除它

2 个答案: