更新mysql值C#后连接错误

Question

所以我的想法是一旦用户登录，它将在我的 mysql 中为另一个表和在线值添加 +1。我已经完成了如下代码。一旦我有调试。我已经插入了用户名和密码，但是一旦我按下登录按钮，它就会显示错误连接。我确定我在代码中做错了，但无法对其进行排序。所以我想从你们那里得到帮助。谢谢

        private void loginBtn_Click(object sender, EventArgs e)
        {
            try
            {
                if (txtUsername.Text != "" && txtPassword.Text != "")
                {

                    con.Open();
                    string query = "SELECT id,username,password,email,fullname,company,uploads,avatar,account_type FROM users WHERE username ='" + txtUsername.Text + "' AND password ='" + txtPassword.Text + "'";
                    MySqlDataReader row;
                    row = con.ExecuteReader(query);
                    if (row.HasRows)
                    {
                        while (row.Read())
                        {
                            Properties.Settings.Default.username = row["username"].ToString();
                            Properties.Settings.Default.email = row["email"].ToString();
                            Properties.Settings.Default.fullname = row["fullname"].ToString();
                            Properties.Settings.Default.company = row["company"].ToString();
                            Properties.Settings.Default.uploads = row["uploads"].ToString();
                            Properties.Settings.Default.user_avatar = row["avatar"].ToString();

                            MySqlCommand newcmd = new MySqlCommand("UPDATE company SET online = online + 1 WHERE name = '" + row["company"].ToString() + "'");

                            try
                            {
                                newcmd.ExecuteNonQuery();
                            }
                            catch (MySqlException ex)
                            {
                                con.Close();
                                MessageBox.Show(ex.Number.ToString() + " -> " + ex.Message.ToString());
                                return;
                            }
                        }
                        this.Hide();
                        dashboard dash = new dashboard();
                        dash.Show();
                    }
                    else
                    {
                        MessageBox.Show("Nie znaleziono użytkownika", "Information");
                    }
                }
                else
                {
                    MessageBox.Show("Nazwa użytkownika lub hasło jest nie poprawne", "Information");
                }
            }
            catch
            {
                MessageBox.Show("Błąd połączenia", "Information");
            }

Answer 1

对于您的问题，您登录时出现连接错误。

错误可能是已经有一个打开的数据读取器与此连接关联

必须关闭，所以关闭数据读取器连接。

你可以试试下面的代码来获取它。

     private void btn_Submit_Click(object sender, EventArgs e)
        {

            conn.Open();
            try
            {
                if (txtUsername.Text != "" && txtPassword.Text != "")
                {


                    string query = "SELECT id,username,password,email,fullname,company,uploads,avatar,account_type FROM users WHERE username ='" + txtUsername.Text + "' AND password ='" + txtPassword.Text + "'";
                    MySqlCommand cmd = new MySqlCommand(query, conn);
cmd.ExecuteScalar();
                    MySqlDataReader row;
                    row = cmd.ExecuteReader();
                    string company=null;
                    if (row.HasRows)
                    {
                        while (row.Read())
                        {
                            Properties.Settings.Default.username = row["username"].ToString();
                            Properties.Settings.Default.email = row["email"].ToString();
                            Properties.Settings.Default.fullname = row["fullname"].ToString();
                            Properties.Settings.Default.company = row["company"].ToString();
                            Properties.Settings.Default.uploads = row["uploads"].ToString();
                            Properties.Settings.Default.user_avatar = row["avatar"].ToString();
                            company = row["company"].ToString();

                            MessageBox.Show(row["company"].ToString(), "Note", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        }
                        row.Close();
                            cmd.CommandText = "UPDATE company SET online = online + 1 WHERE name = '" + company + "'";
                            try
                            {
                                cmd.ExecuteNonQuery();
                            }
                            catch (MySqlException ex)
                            {
                                MessageBox.Show(ex.Number.ToString() + " -> " + ex.Message.ToString());
                            }                
                        this.Hide();
                        dashboard dash = new dashboard();
                        dash.Show();

                    }
                    else
                    {
                        MessageBox.Show("Nie znaleziono użytkownika", "Information");
                    }
                }
                else
                {
                    MessageBox.Show("Nazwa użytkownika lub hasło jest nie poprawne", "Information");
                }
            }
            catch 
            {
                MessageBox.Show("Błąd połączenia", "Information");
            }
            finally
            {
                conn.Close();
            }
       }

结果：