DAL/MailService.cs

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using Model;
using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DAL
{
    public class MailService
    {
        //获取我的学生账号
        public static List<Mail> getSnumList(Mail mai)
        {
            string sql = $"select distinct s.StudentNum  from LessonSelect ls left join Lessoninfo l on ls.id=l.id left join Studentinfo s on s.StudentName=ls.StudentName where l.Teacher='{mai.Sender}'";
            SqlDataReader dr = DBHelper.getData(sql);
            List<Mail> list = new List<Mail>();
            Mail m = null;
            while (dr.Read())
            {
                m = new Mail()
                {
                    ConsigNum = dr.GetInt32(0)
                };
                list.Add(m);
            }
            dr.Close();
            return list;
        }
        //放入回收站
        public static bool Mailhuishou(int id)
        {
            string sql = $"UPDATE [dbo].[Mailinfo] SET [MailState] = '回收' where id='{id}'";
            return DBHelper.updateData(sql);
        }
        //标为未读
        public static bool Mailweidu(int id)
        {
            string sql = $"UPDATE [dbo].[Mailinfo] SET [MailState] = '未读' where id='{id}'";
            return DBHelper.updateData(sql);
        }
        //查询有多少条未读消息
        public static Mail getCount(int ConsigNum)
        {
            string sql = $"select COUNT(*) from Mailinfo where MailState='未读' and ConsigNum='{ConsigNum}'";
            SqlDataReader dr = DBHelper.getData(sql);
            Mail mai = null;
            if (dr.Read())
            {
                mai = new Mail()
                {
                    CountMail=dr.GetInt32(0)
                };
            }
            dr.Close();
            return mai;
        }
        //邮件查看后变为已读
        public static bool updata(int id)