如何避免可能的多重枚举警告

IEnumerable 两次:

var redefineSchoolDatas = group.Select(g =>
{
    var elementsInGroup = g.ToList();
    return new RedefineSchoolData
    {
        ClassName = g.Key,
        Count = elementsInGroup.Count,
        Students = elementsInGroup.Select(s => new Student
        {
            StudentName = s.StudentName,
            StudentAge = s.StudentAge
        }).ToList(),
    }
}).ToList();

不过,我建议你不要 Count RedefineSchoolData 班级。维护 计数 与收藏分开( Students )不是个好主意:假设你删除了一个学生-那么你还需要记住更新 计数

class RedefineSchoolData
{
    public Student Students { get; set; }
    public int Count => Students.Count;
    // Other properties kept out for brevity
}

// Now your LINQ statements could be:
var redefineSchoolDatas = group.Select(g =>
    new RedefineSchoolData
    {
        ClassName = g.Key,
        Students = g.Select(s => new Student
        {
            StudentName = s.StudentName,
            StudentAge = s.StudentAge
        }).ToList(),
    }).ToList();