public  class LoginDA
    {
      private   DataClasses1DataContext _context;
      public LoginDA()
      {
         _context = new DataClasses1DataContext();
      }
       //查询全部数据
       public List<login> select()
       {
           List<login> list = new List<login>();
           list = _context.login.ToList();
           return list;
       }
       //根据用户名查询
       public List<login> select(string userName)
       {
           List<login> data = _context.login.Where(r=>r.username==userName).ToList();
           return data;
       }
       //添加数据
       public void insert(login data)
       {
         
           _context.login.InsertOnSubmit(data);
           _context.SubmitChanges();

       }
       //删除数据
       public void deleteByName(string userName)
       {
           //利用Single函数根据主键返回一个对象，注意udata中存储的是缓存数据里对象的地址，只有这样才能删除缓存数据里的对象，修改数据是同样的道理
           login data= _context.login.Single(r => r.username == userName);
           _context.login.DeleteOnSubmit(data);
           _context.SubmitChanges();
       }
       //修改数据
       public void update(login data)
       {
           
           login udata = _context.login.Single(r=>r.username==data.username);
           if (udata != null)
           {
               udata.username = data.username;
               udata.pwd = data.pwd;
           }
           _context.SubmitChanges();
       }
       //模糊查询
       public List<login> selectByMohu(string userName)
       {
           return _context.login.Where(r => r.username.Contains(userName)).ToList();
       }


       public login select1(string userName)
       {
           //返回集合中的一条数据
           return _context.login.Where(r => r.username == userName).First();
       }
    }