编写数据库增、删、改操作方法

 //得到所有用户列表
        public IList<Users> getAllUsers()
        {
            string sql = "select users.*,u.unitName,R.* from Users as users left join Unit as u on users.unitId = u.id left join Roles R on users.roleId = R.id";
            IList<Users> list = new List<Users>();
            using (SqlDataReader reader = DBHelper.ExecuteReader(sql))
            {
                while (reader.Read())
                {
                    Users model = new Users();
                    model.Id = Convert.ToInt32(reader["Id"]);
                    model.Account = reader["Account"].ToString();
                    model.Password = reader["Password"].ToString();
                    model.Username = reader["Username"].ToString();
                    model.Telephone = reader["Telephone"].ToString();
                    model.Unitid = Convert.ToInt32(reader["unitId"]);
                    model.Roleid = (int)reader["Roleid"];

                    Unit unit = new Unit();
                    unit.UnitName = reader["unitName"].ToString();
                    model.Unit = unit;

                    Roles role = new Roles();
                    role.Role = reader["role"].ToString();
                    role.Power = reader["power"].ToString();
                    model.Role = role;

                    list.Add(model);

                }
            }
            return list;
        }
/// <summary>
     /// 添加用户
     /// </summary>
     /// <param name="user"></param>
     /// <returns></returns>
            public int AddUser(Users user)
            {
                string sql =
                    "insert into Users (account, password, username, telephone, unitid, roleid)" +
                    " values (@account, @password, @username, @telephone, @unitid, @roleid)";
                sql += " ; SELECT @@IDENTITY";

                SqlParameter[] para = new SqlParameter[]
                {
                    new SqlParameter("@account", user.Account),   
                    new SqlParameter("@password", user.Password),     
                    new SqlParameter("@username", user.Username),
                    new SqlParameter("@telephone", user.Telephone),
                    new SqlParameter("@unitid", user.Unit),
                    new SqlParameter("@roleid", user.Roleid)
                };
                int newId = 0;
                newId = DBHelper.ExecuteScalar(sql, para);
                return newId;
            }

 /// <summary>
            /// 更新密码
            /// </summary>
            public int UpdatePwd(int id, string pwd)
            {
                string strsql = "update users set password='" + pwd + "' where id= " + id;
                              
                int i = Convert.ToInt32(DBHelper.ExecuteCommand(strsql.ToString()));

                return i;
               
            }
  //根据用户id 删除用户
            public int DeleteUser(int id)
            {
                string sql = "delete from users where id=" + id;
                int newId = 0;
                newId = DBHelper.ExecuteScalar(sql);
                return newId;
            }