使用Mysqldatareader访问行

Question

有没有办法访问和赋值高列的第(i+1)或第(i-1)个值？

我的代码如下：

public static List<db1> Read_DB1(string date, MySqlConnection conn)
{
string sql = "select * from table2replica where Date=\'" + date + "\'"; // loads for a particular date


            List<db1> db1List = new List<db1>();
            using (MySqlCommand cmd = new MySqlCommand(sql, conn))
            {
                using (MySqlDataReader reader = cmd.ExecuteReader())
                {
                    if (reader != null)
                    {
                        while (reader.Read())
                        {
                            db1 db1Obj = new db1();
                            db1Obj.Symbol = reader["Stock"].ToString();
                            db1Obj.Date = Convert.ToDateTime(reader["Date"]);
                            db1Obj.Open = Convert.ToDouble(reader["Open"]);
                            db1Obj.High = Convert.ToDouble(reader["High"]);
                            db1Obj.Low = Convert.ToDouble(reader["Low"]);
                            db1List.Add(db1Obj);

                      }
                }
            }

我是否应该引用并分配下一行的值，使用：

db1Obj.HighNextRow = Convert.ToDouble(reader["High"]+1)

或

db1Obj.PreviousRow = Convert.ToDouble(reader["High"+1])

Answer 1

DbDataReader只能向前移动，并且在任何给定的循环中，它只知道当前记录。不能跳回读取上一条记录的字段，也不能跳转到读取下一条记录的字段。

但是，您可以自己跟踪此以前的记录，使以前的db1Obj实例保持活动状态。

db1 db1Obj = null;
db1 prevObj = null;
while (reader.Read())
{
    db1Obj = new db1();
    db1Obj.Symbol = reader["Stock"].ToString();
    db1Obj.Date = Convert.ToDateTime(reader["Date"]);
    db1Obj.Open = Convert.ToDouble(reader["Open"]);
    db1Obj.High = Convert.ToDouble(reader["High"]);
    db1Obj.Low = Convert.ToDouble(reader["Low"]);
    if(prevObj != null) 
    {
        prevObj.HighNextRow = db1Obj.High;
        db1Obj.PrevRow = prevObj.High;
    }
    prevObj = db1Obj;
    db1List.Add(db1Obj);
}
if(prevObj != null && db1Obj != null) 
{
   prevObj.HighNextRow = db1Obj.High;
   db1Obj.PrevRow = prevObj.High;
}