使用 Linq 更新列表列值，如果值为空

Question

我有List<Student>多个记录

public class Student

{            

    public int? StudentId { get; set; }

    public string StudentName { get; set; }

    public int? AttendanceStatusId { get; set; }

    public string AttendanceStatusDes { get; set; }     

}

在将数据发布到服务器时，有时AttendanceStatusId和AttendanceStatusDes会出现null。当 List 记录中的这 2 个值为空时，我想设置AttendanceStatusId=1&AttendanceStatusDes="Present" 如何使用 Linq 查询来做到这一点。谢谢

Answer 1

不要使用 LINQ 或循环，而是为您的模型设置默认值。通过这种方式，您将始终确保按预期获得模型，并且无需到处乱搞所有学生列表。这可能不适用于 OP 案例，但值得一提的是，如果您的类是可序列化的，那么使用这种“技术”您仍然可以获得默认值。public class Student{&nbsp; &nbsp; public int? StudentId { get; set; }&nbsp; &nbsp; public string StudentName { get; set; }&nbsp; &nbsp; private int? _attendanceStatusId;&nbsp; &nbsp; public int? AttendanceStatusId&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; //you can use null coalescing operator here&nbsp; &nbsp; &nbsp; &nbsp; //like this: get { return _attendanceStatusId ?? 1; }&nbsp; &nbsp; &nbsp; &nbsp; get { return _attendanceStatusId == null ? 1 : _attendanceStatusId; }&nbsp; &nbsp; &nbsp; &nbsp; set { _attendanceStatusId = value; }&nbsp; &nbsp; }&nbsp; &nbsp; private string _attendanceStatusDes;&nbsp; &nbsp; public string AttendanceStatusDes&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; //Or get { return _attendanceStatusDes ?? "Present" }&nbsp; &nbsp; &nbsp; &nbsp; get { return _attendanceStatusDes == null ? "Present" : _attendanceStatusDes; }&nbsp; &nbsp; &nbsp; &nbsp; set { _attendanceStatusDes = value; }&nbsp; &nbsp; }}

Answer 2

获取过滤列表：var missingStatus = Students.Where(s => !s.AttendanceStatusId.HasValue && AttendanceStatusDes == null);然后迭代该列表，编辑这些项目的值。foreach(var student in missingStatus){&nbsp; student.AttendanceStatusId = 1;&nbsp; student.AttendanceStatusDes = "Present";}这有帮助吗？您当然可以在列表中的 foreach 中执行此操作，但我不建议这样做：Students.Where(s => !s.AttendanceStatusId.HasValue && AttendanceStatusDes == null)&nbsp; .ToList()&nbsp; .ForEach(s => {&nbsp; &nbsp; &nbsp; s.AttendanceStatusId = 1;&nbsp; &nbsp; &nbsp; s.AttendanceStatusDes = "Present";&nbsp; });