Connection must be valid and open - mysql

Question

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
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;
}
}
}

Answer 1

A couple of things;
You're using ExecuteNonQuery for a Query. Try for example ExecuteReader instead.
You're not setting a connection for your DbCommand, so executing it won't find the database.
Try this instead;
MySqlConnection dbcon = new MySqlConnection(db);
string sql = "SELECT * FROM members";
MySqlCommand cmd = new MySqlCommand(sql, dbcon); //<-- pass connection to command
Your current code;
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.