C# 按多列返回linq组的类型

我有以下代码：

 var studentClassAttendancesGrouped =
                            classAttendanceByCriteria.OrderBy(x => x.Lecture.Id).GroupBy(x => new { x.Lecture, x.Teacher });

我试图从一个方法返回

studentClassAttendancesGrouped

。但我无法确定该方法的返回类型。

GroupBy的

重载将返回
IEnumerable
，如图所示

您只需要使用投影您的可枚举项，当然，您必须在末尾调用以执行查询并创建列表：

var res = classAttendanceByCriteria.OrderBy(x => x.Lecture.Id)
                                   .GroupBy(x => new { x.Lecture, x.Teacher })
                                   .Select(x => new {x.Key.Lecture, x.Key.Teacher})
                                   .ToList();

但是，上面的代码创建了一个匿名类型列表。如果要从方法返回上述语句，则需要使用或创建自定义对象并返回以下列表：

public class LectureTeacher
{
    public string Lecture { get; set; }
    public string Teacher { get; set; }
}

public List<LectureTeacher> GetDogsWithBreedNames()
{
    var res = classAttendanceByCriteria.OrderBy(x => x.Lecture.Id)
                                       .GroupBy(x => new { x.Lecture, x.Teacher })
                                       .Select(x => new LectureTeacher {Lecture  = x.Key.Lecture, Teacher  = x.Key.Teacher})
                                       .ToList();

    return res;
}

我建议您创建一个自定义类，并从方法返回它：-

IEnumerable<CustomType> studentClassAttendancesGrouped =
       classAttendanceByCriteria.OrderBy(x => x.Lecture.Id)
       .GroupBy(x => new { x.Lecture, x.Teacher })
      .Select(x => new CustomType { Lecture = x.Key.Lecture, Teacher = x.Key.Teacher });

您可以根据需要添加更多列，最后从方法返回
IEnumerable

因此，您的方法如下所示：-

public IEnumerable<CustomType> MyMethod()
{
    return classAttendanceByCriteria.OrderBy(x => x.Lecture.Id)
       .GroupBy(x => new { x.Lecture, x.Teacher })
       .Select(x => new CustomType { Lecture = x.Key.Lecture, Teacher = x.Key.Teacher });
}

public IEnumerable MyMethod（）
{
return classAttendanceByCriteria.OrderBy（x=>x.touch.Id）
.GroupBy（x=>新{x.讲座，x.教师}）
.Select（x=>newcustomtype{teachment=x.Key.Teacher，Teacher=x.Key.Teacher}）；
}

public class CustomType 
{
   public string Lecture {get; set; }
   public string Teacher {get; set; }
}

public IEnumerable<CustomType> MyMethod()
{
    return classAttendanceByCriteria.OrderBy(x => x.Lecture.Id)
       .GroupBy(x => new { x.Lecture, x.Teacher })
       .Select(x => new CustomType { Lecture = x.Key.Lecture, Teacher = x.Key.Teacher });
}