Question

有一个班级

Public class Student
{
  int id;
  int rollNum;
  String Name;
}

方法

Public List<Student> GetAllStudents()
{
  var studentList = GetMeAll(); // Simple select * query to get all students
  //unfortunately i can't make changes in this method so have to write a linq query to       //filter data.
  //getting int array ids correctly from some method
   var filterList = FilterStudentsByID(ids,StudentList);
}

我想编写一个方法，将int数组作为输入并返回List

Public List<Student> FilterStudentsByID(int[] ids,List<student> studentList)
{
  //There should be a linq query , but I am new to linq so don't know how to write this.
  Var list = from  studentList in ..... don't know much;
}

编写查询时的任何帮助。谢谢大家的答案，我也在寻找保持大型记录列表的表现？如果你可以添加我简单的查询解释将在内部工作会很棒吗？

Answer 1

如果您希望从ids数组中出现id的列表中找到那些学生，那么：

var list = from s in stundentList
           where ids.Contains(s.ID)
           select s;

Answer 2

试

Var list = studentList.Where(s=>ids.Contains(s.id)).ToList();

Answer 3

我认为已经给出的答案足够快，但以防万一在测试后你发现它太慢了：你可以尝试在进行搜索之前将学生列表转换为字典。< / p>

你应该只在经过仔细的时间测试之后使用它，因为对于大多数情况来说它可能会慢得多！

public static List<Student> FilteredStudents(int[] targetIds)
{
    var allStudents = GetAllStudents().ToDictionary(student => student.id);
    var result = new List<Student>();

    foreach (int id in targetIds)
    {
        Student student;

        if (allStudents.TryGetValue(id, out student))
        {
            result.Add(student);
        }
    }

    return result;
}

在LINQ Query的where子句中传递int数组

3 个答案: