/// <summary>匯入Excel資料到資料庫
        /// 
        /// </summary>
        /// <param name="file">檔案</param>
        public ActionResult ImportExcel(HttpPostedFileBase file)
        {
            if (file != null)
            {
                bool exportColumnName = true;
                Aspose.Cells.Workbook workbook = new Aspose.Cells.Workbook();
                workbook.Open(file.FileName);
                Aspose.Cells.Worksheet worksheet = workbook.Worksheets[0];
                Cells cells = worksheet.Cells;DataTable datatable = cells.ExportDataTableAsString(0, 0, cells.MaxDataRow + 1, cells.MaxDataColumn + 1, exportColumnName);//這裡用到Aspose.Cells的ExportDataTableAsString方法來讀取excel資料
                 //對班級進行分組
                var groupByClass = datatable.Rows.Cast<DataRow>().GroupBy(u => u["班級"]);
                //匯入一次資料就清空班級表
                string deleteSql = "TRUNCATE TABLE dbo.Classes";
                db.Database.ExecuteSqlCommand(deleteSql);

                foreach (var item in groupByClass)
                {
                    Classes classes = new Classes();
                    classes.ClassName = item.Key.ToString();
                    db.Classes.Add(classes);
                    db.SaveChanges();

                }
                string[] fileds = new string[] { "班級" }; // 分組條件
                List<DataTable> grouped = new List<DataTable>(); // 儲存分組結果

                //得到分組資料，並存到grouped中
                GroupDataRows(datatable.Rows.Cast<DataRow>(), grouped, fileds, 0, datatable);

                // 輸出分組
                foreach (DataTable dt in grouped)
                {
                    foreach (DataRow row in dt.Rows)
                    {
                        string className = row["班級"].ToString();
                        int classID = db.Classes.Where(cl => cl.ClassName == className).FirstOrDefault().ID;
                        row.BeginEdit();
                        row["班級"] = classID;
                        if (row["性別"].ToString() == "男")
                        {
                            row["性別"] = 0;
                        }
                        else
                        {
                            row["性別"] = 1;
                        }
                        User user = new User();
                        user.UserName = row["賬號"].ToString();
                        user.Password = row["密碼"].ToString();
                        user.NickName = row["呢稱"].ToString();
                        user.RoleID = 4;
                        user.Sex = int.Parse(row["性別"].ToString());
                        if (row["年齡"].ToString() == "")
                        {
                            user.Age = null;
                        }
                        else
                        {
                            user.Age = int.Parse(row["年齡"].ToString());
                        }
                        if (row["學校"].ToString() == "")
                        {
                            user.School = null;
                        }
                        else
                        {
                            user.School = row["學校"].ToString();
                        }
                        if (row["積分"].ToString() == "")
                        {
                            user.Coins = null;
                        }
                        else
                        {
                            user.Coins = int.Parse(row["積分"].ToString());
                        }

                        user.ClassID = int.Parse(row["班級"].ToString());

                        db.User.Add(user);
                        db.SaveChanges();
                    }
                }
                return RedirectToAction("StudentIndex");
            }
            else
            {
                return RedirectToAction("StudentIndex");
            }

        }
 	/// <summary>把dataTable資料通過某列分組，再把分組資料存到LIst<Datatable>中
        /// 
        /// </summary>
        /// <param name="source">資料中每行資料</param>
        /// <param name="destination">分組後資料存入的Datatable</param>
        /// <param name="groupByFields">分組欄位陣列</param>
        /// <param name="fieldIndex"></param>
        /// <param name="schema">資料集</param>
        public static void GroupDataRows(IEnumerable<DataRow> source, List<DataTable> destination, string[] groupByFields, int fieldIndex, DataTable schema)
        {
            if (fieldIndex >= groupByFields.Length || fieldIndex < 0)
            {
                DataTable dt = schema.Clone();
                foreach (DataRow row in source)
                {
                    DataRow dr = dt.NewRow();
                    dr.ItemArray = row.ItemArray;
                    dt.Rows.Add(dr);
                }

                destination.Add(dt);
                return;
            }

            var results = source.GroupBy(o => o[groupByFields[fieldIndex]]);
            foreach (var rows in results)
            {
                GroupDataRows(rows, destination, groupByFields, fieldIndex + 1, schema);
            }

            fieldIndex++;
        }