连接必须有效并打开mysql [英] Connection must be valid and open mysql

问题描述

我在修复mysql db中的列中的最后一个值时遇到问题。

我得到连接必须是有效的并且打开错误。

有人可以请帮助？

谢谢



我的尝试：

I am having a problem in retirieving the last value in a column in mysql db.
I am getting connection must be valid and open error.
Can someone please help?
Thanks

What I have tried:

String connString = System.Configuration.ConfigurationManager.ConnectionStrings["web"].ToString();
        using (MySqlConnection con = new MySqlConnection(connString))
        {
            using (MySqlCommand cmd = new MySqlCommand("SELECT TOP 1 idProyecto FROM proyectos order by idProyecto DESC LIMIT 1"))
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = conn;
                con.Open();
                val1 = cmd.ExecuteScalar().ToString();
                con.Close();
                return val1;

            }
        }

推荐答案

Quote：

cmd.Connection = conn;

cmd.Connection = conn;

您已将连接对象声明为con，然后告诉您的命令对象使用连接对象称为conn。



由于这实际编译了，看来你在同一范围或更高的范围内有一个名为conn的另一个连接对象等级范围。这样做是不好的做法。

You've declared your connection object as "con" and then told your command object to use a connection object called "conn".

Since this actually compiled, it appears you've got another connection object called "conn" somewhere above this in the same scope or in a higher level scope. That would be bad practice to have that.

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