Access获取新插入数据的自增长主键Id

　　sqlserver有output，Oracle有Sequence。Access用下面的方法，注意两次查询用一个connection：

 public int InsertEx(User user)
 {
     int id = -;

     using (OleDbConnection conn = new OleDbConnection(AccessHelper.connectionString))
     {
         conn.Open();

         OleDbCommand cmd = new OleDbCommand { Connection = conn, CommandType = CommandType.Text };

         string commandText =
             $"insert into tb_user (username,userpassword,insdate,dr) values (@username, @userpwd, Date(), 0)";
         List<OleDbParameter> paras = new List<OleDbParameter>
                                      {
                                          new OleDbParameter("username", user.UserName),
                                          new OleDbParameter("userpwd", user.UserPassword)
                                      };

         cmd.CommandText = commandText;
         cmd.Parameters.AddRange(paras.ToArray());
         cmd.ExecuteNonQuery();

         cmd.CommandText = "select @@identity as id";
         cmd.Parameters.Clear();
         id = Convert.ToInt32(cmd.ExecuteScalar());
     }

     return id;
 }