我在使用用户密码编码示例时遇到问题

Question

Using this earlier question I need a bit of help

使用上面链接中的第二个答案，我必须为 MySQL 更新它

 private void btLogin_Click(object sender, EventArgs e)
        {
            string connectionString;
            connectionString = "SERVER=" + server + ";" + "DATABASE=" + database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";";

            connection = new MySqlConnection(connectionString);
            using (var con = new MySqlConnection(connectionString));
            {
                using (var command = new MySqlCommand(connection = con))
                {
                    con.Open();

                    command.CommandText = @"SELECT level FROM userTable WHERE user=@username, password=@password";
                    command.Parameters.AddWithValue("@username", lbUser.Text);
                    command.Parameters.AddWithValue("@password", tbPassword.Text);

                    var strLevel = command.ExecuteScalar();

                    if (strLevel == DBNull.Value || strLevel == null)
                    {
                        MessageBox.Show("Invalid username or password");
                        return;
                    }
                    else
                    {
                        MessageBox.Show("Successfully login");
                        Hide(); // hide this form and show another form
                    }

                }
            }
        }

一切看起来都不错，但是这个

 using (var con = new MySqlConnection(connectionString));
            {
                using (var command = new MySqlCommand(connection = con))
                {
                    con.Open();

它说 con 不存在。不知道用那个井看问题。

Answer 1

MySqlCommand 构造函数的第一个参数是命令文本。如果您将代码更改为以下内容，它应该可以工作：

con.Open();
using (var command = new MySqlCommand())
{
    command.Connection = con;
    command.CommandText = @"SELECT level FROM userTable WHERE user=@username AND password=@password";