连接必须有效且开放

Connection must be valid and open. where is the problem ? .net Frmework version 2.0 Connection must be valid and open. where is the problem ? .net Frmework version 2.0 Connection must be valid and open. where is the problem ? .net Frmework version 2.0

连接必须有效且开放。问题出在哪儿 ? .net Frmework 2.0版连接必须有效且开放。问题出在哪儿 ? .net Frmework 2.0版连接必须有效且开放。问题出在哪儿 ? .net Frmework 2.0版

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Security.Cryptography;
using MySql.Data.MySqlClient;
    namespace Student_Portal_Password
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        public static string GetMd5Hash(string input)
        {
            MD5 md5Hash = MD5.Create();
            // Convert the input string to a byte array and compute the hash.
            byte[] data = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(input));

            // Create a new Stringbuilder to collect the bytes
            // and create a string.
            StringBuilder sBuilder = new StringBuilder();

            // Loop through each byte of the hashed data 
            // and format each one as a hexadecimal string.
            for (int i = 0; i < data.Length; i++)
            {
                sBuilder.Append(data[i].ToString("x2"));
            }

            // Return the hexadecimal string.
            return sBuilder.ToString();
        }
        public  void check()
        {
            if (txtid.Text == "")
            {
                MessageBox.Show("Please enter Student ID ", MessageBoxIcon.Warning.ToString(), MessageBoxButtons.OK);
            }
            else if (txtpassword.Text == "")
            {
                MessageBox.Show("Please enter new password", MessageBoxIcon.Warning.ToString(), MessageBoxButtons.OK);
            }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            try
            {

 //check();
            txtpassword.Text.Trim();
            string hash = GetMd5Hash(txtpassword.Text);

            string db = "server=localhost;uid=root;password=usbw;database=dum;";
            MySqlConnection dbcon = new MySqlConnection(db);
            MySqlCommand cmd = new MySqlCommand(db);

            dbcon.Open();
            cmd.CommandText = "SELECT * FROM members;";
            cmd.ExecuteNonQuery();
                          MessageBox.Show("Success!");
                          dbcon.Close();
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void txtid_KeyPress(object sender, KeyPressEventArgs e)
        {
            const char Delete = (char)8;
            e.Handled = !Char.IsDigit(e.KeyChar) && e.KeyChar != Delete;
        }
    }
}

1 个解决方案

#1

A couple of things;

一些事情;

You're using ExecuteNonQuery for a Query. Try for example ExecuteReader instead.

您正在使用ExecuteNonQuery进行查询。请尝试使用示例ExecuteReader。

You're not setting a connection for your DbCommand, so executing it won't find the database.
Try this instead;

您没有为DbCommand设置连接,因此执行它将无法找到数据库。试试这个;

MySqlConnection dbcon = new MySqlConnection(db);
string sql = "SELECT * FROM members";
MySqlCommand cmd = new MySqlCommand(sql, dbcon); //<-- pass connection to command

Your current code;

您当前的代码;

MySqlCommand cmd = new MySqlCommand(db);

...passes in the connection string as the SQL to execute, and does not associate the command with any database connection. That will give the error you're asking about.

...将连接字符串作为要执行的SQL传递,并且不将该命令与任何数据库连接相关联。这会给你提出的错误。

#1