Question

我似乎在关闭数据库连接（Program.DB_CONNECTION）时出现问题。

当我关闭表单时，我运行Program.DB_CONNECTION.Close，但是这个dosnt似乎关闭了连接，因为数据库锁文件仍然存在，我无法删除数据库。

任何人都可以看到我做错了数据库不能关闭吗？

private void update_gic_attendances()
    {
        OleDbCommand com = new OleDbCommand("SELECT count(*), [Squadron] FROM Personnel WHERE [Position] = ? and [Current?] = TRUE GROUP BY [Squadron]", Program.DB_CONNECTION);
        com.Parameters.Add(new OleDbParameter("", PositionIDs.GIC));

        OleDbDataReader dr = com.ExecuteReader();

        while (dr.Read())
        {
            try
            {
                OleDbCommand com2 = new OleDbCommand("SELECT * FROM GIC_Attendances WHERE [Attendance_Date] = ? AND [Squadron] = ?", Program.DB_CONNECTION);
                com2.Parameters.Add(new OleDbParameter("", DateTime.Today.Date));
                com2.Parameters.Add(new OleDbParameter("", dr.GetInt32(1)));

                OleDbDataReader dr2 = com2.ExecuteReader();

                if (dr2.HasRows)
                {
                    //update the number of attendees
                    OleDbCommand com3 = new OleDbCommand("UPDATE GIC_Attendances SET [Number_Attended] = ? WHERE [Attendance_Date] = ? AND [Squadron] = ?", Program.DB_CONNECTION);
                    com3.Parameters.Add(new OleDbParameter("", dr.GetInt32(0)));
                    com3.Parameters.Add(new OleDbParameter("", DateTime.Today.Date));
                    com3.Parameters.Add(new OleDbParameter("", dr.GetInt32(1)));

                    com3.ExecuteNonQuery();
                }
                else
                {
                    OleDbCommand com3 = new OleDbCommand("INSERT INTO GIC_Attendances ([Attendance_Date], [Squadron], [Number_Attended], [Number_Expected], [AddedOnSlave]) VALUES (?, ?, ?, ?, TRUE)", Program.DB_CONNECTION);
                    com3.Parameters.Add(new OleDbParameter("", DateTime.Today.Date));
                    com3.Parameters.Add(new OleDbParameter("", dr.GetInt32(1)));
                    com3.Parameters.Add(new OleDbParameter("", dr.GetInt32(0)));
                    com3.Parameters.Add(new OleDbParameter("", 4));

                    com3.ExecuteNonQuery();
                }

                dr2.Close();
            }
            catch
            {
            }
        }

        dr.Close();
    }

Answer 1

如评论中所述，您需要关闭并处理连接。拥有一个保持连接的全局变量不是一个好的模式，因为它总是很难正确地销毁变量。

你可以尝试这样的东西来证明这一点

private void update_gic_attendances()
{
    using(OleDbConnection cn = new OleDbConnection(....your connection string...))
    using(OleDbCommand com = new OleDbCommand(....., cn))
    {
         cn.Open();
         .....
         using(OleDbDataReader dr1 = com.ExecuteReader())
         {
            while(dr1.Read())
            {
                using(OleDbCommand com2 = new OleDbCommand(...., cn);
                using(OleDbDataReader dr2 = com2.ExecuteReader())
                {
                   ....
                   if(dr2.HasRows)
                   {
                        using(OleDbCommand com3 = new OleDbCommand(....., cn)
                        {
                           ....
                          com3.ExecuteNonQuery();
                        }
                   }
                   else
                   {
                        using(OleDbCommand com3 = new OleDbCommand(....., cn))
                        {
                            com3.ExecuteNonQuery();
                        }
                   }
                }
            }

        }
    }
}

现在连接是方法的本地连接。它被创建并包含在using语句中，该语句将在using块的出口处关闭并销毁它。而读者和命令等其他一次性物体也是如此。在此代码的末尾，连接已关闭并处理，文件不应再被锁定（除非您在某处打开了另一个连接）

但是，在你的第一个查询中，有些东西似乎不正确您调用SELECT COUNT（*）语句，但这只返回满足查询WHERE子句的数字或记录，而不是整行。然后使用DataReader循环遍历此查询结果，最糟糕的是，您尝试为第一个和第二个字段调用GetInt32。但第二个不存在。

数据库连接没有关闭窗体

1 个答案: