c# - 如何修复此 MySql 异常？ [C#]

Question

所以我尝试创建一个使用 MySql 数据库的简单登录表单。我在 Hostinger 上创建了一个简单的 MySql 数据库和一个名为 users 的表，其中包含两列:用户名列和密码列。然后我编码如下:

namespace MySql_Login_Form
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void loginBtn_Click(object sender, EventArgs e)
        {
            try {
                MySqlConnection connection = new MySqlConnection("Server=mysql.hostinger.nl;Database=u725015652_users;User Id=u725015652_gewoo;Password=[MyPassword];");
                MySqlDataAdapter adapter;
                DataTable table = new DataTable();
                adapter = new MySqlDataAdapter("SELECT `username`, `password` FROM `users` WHERE `username` = '" + usernameTxt.Text + "' AND `password` = '" + passwordTxt.Text + "'", connection);
                adapter.Fill(table);

                if (table.Rows.Count >= 1)
                {
                    MessageBox.Show("Succeed");
                }
                else
                {
                    MessageBox.Show("False");
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }
    }
}

我的数据库详细信息:

当我运行代码时，出现此错误:

MySql.Data.MySqlClient.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts. ---> System.Net.Sockets.SocketException (0x80004005): Host is unknown
   at System.Net.Dns.GetAddrInfo(String name)
   at System.Net.Dns.InternalGetHostByName(String hostName, Boolean includeIPv6)
   at System.Net.Dns.GetHostEntry(String hostNameOrAddress)
   at MySql.Data.Common.MyNetworkStream.CreateStream(MySqlConnectionStringBuilder settings, Boolean unix)
   at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.NativeDriver.Open()
   at MySql.Data.MySqlClient.Driver.Open()
   at MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.MySqlPool.GetPooledConnection()
   at MySql.Data.MySqlClient.MySqlPool.TryToGetDriver()
   at MySql.Data.MySqlClient.MySqlPool.GetConnection()
   at MySql.Data.MySqlClient.MySqlConnection.Open()
   at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables, Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataTable dataTable)
   at MySql_Login_Form.Form1.loginBtn_Click(Object sender, EventArgs e) in C:\.....\Login Form\MySql Login Form\Form1.cs:Line 28

第 28 行是这一行:

adapter.Fill(table);

Answer 1

您无法连接到 MySql 服务器。最有可能需要提供端口号Server=mysql.hostinger.nl:12345

我有点想知道您是否真的也有 mysql.hostinger.nl 的 DNS 条目。如果没有，您要么需要一个 DNS 条目，要么只使用 IP 地址。

此外，您的代码容易受到 Sql 注入(inject)的攻击。<​​/p>

adapter = new MySqlDataAdapter("SELECT `username`, `password` FROM `users` WHERE `username` = '" + usernameTxt.Text + "' AND `password` = '" + passwordTxt.Text + "'", connection);

即使不关心安全性，我也建议您修复它。