避免使用参数进行SQL注入？

Question

I have recently adjusted my code to avoid getting SQL injections and got helped with adding parameters but now the code is semi-foreign to me and was wondering what object reference is required for MySqlCommand.Parameters

MySqlParameter parameter = new MySqlParameter();
        parameter.ParameterName = "@userid";
        parameter.MySqlDbType = MySqlDbType.NVarChar;
        parameter.Direction = ParameterDirection.Input;
        parameter.Value = this.userid_txt.Text;
        parameter.Value = this.email_txt.Text;
        parameter.Value = this.passone_txt.Text;
        parameter.Value = this.passtwo_txt.Text;
        parameter.Value = this.lastname_txt.Text;
        parameter.Value = this.firstname_txt.Text;

        string Query = "insert into userdatabase.users (userid, email, passone, passtwo, lastname, firstname) values(@userid,@email,@passone,@passtwo,@lastname_txt,@firstname)";
        MySqlCommand.Parameters.AddWithValue("@userid", this.userid_txt.Text);
        MySqlCommand.Parameters.AddWithValue("@email", this.email_txt.Text);
        MySqlCommand.Parameters.AddWithValue("@passone", this.passone_txt.Text);
        MySqlCommand.Parameters.AddWithValue("@passtwo", this.passtwo_txt.Text);
        MySqlCommand.Parameters.AddWithValue("@lastname", this.lastname_txt.Text);
        MySqlCommand.Parameters.AddWithValue("@firstname", this.firstname_txt.Text);

        MySqlConnection conDataBase = new MySqlConnection();
        MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase);
        MySqlCommand cmd = new MySqlCommand(Query, conDataBase);

        cmd.ExecuteNonQuery()

The errors I have state

'MySql.Data.MySqlClient.MySqlDbType' does not contain a defintion for 'NVarChar'

and the main

An object refrence is required for non-static field, method or property 'MySql.Data.MySqlClient.MySqlCommand.Parameters.get'

I am relatively new to using MySql so any help is appreciated

EDIT: New code which causes a fatal error once I click register which connects to my database

MySqlCommand cmdDataBase = new MySqlCommand();
        MySqlParameter parameter = new MySqlParameter();

        string constring = "datasource=127.0.0.1;port=3306;username=root;password=welcome";
        string Query = "insert into userdatabase.users (userid, email, passone, passtwo, lastname, firstname) values(@userid,@email,@passone,@passtwo,@lastname_txt,@firstname)";
        cmdDataBase.Parameters.Add("@userid", MySqlDbType.VarChar).Value = userid_txt.Text;
        cmdDataBase.Parameters.Add("@email", MySqlDbType.VarChar).Value = email_txt.Text;
        cmdDataBase.Parameters.Add("@passone", MySqlDbType.VarChar).Value = passone_txt.Text;
        cmdDataBase.Parameters.Add("@passtwo", MySqlDbType.VarChar).Value = passtwo_txt.Text;
        cmdDataBase.Parameters.Add("@lastname", MySqlDbType.VarChar).Value = lastname_txt.Text;
        cmdDataBase.Parameters.Add("@firstname", MySqlDbType.VarChar).Value = firstname_txt.Text;


        MySqlConnection conDataBase = new MySqlConnection(constring);
        MySqlCommand cmd = new MySqlCommand(Query, conDataBase);

        try {
            conDataBase.Open();
            cmd.ExecuteNonQuery();
            MessageBox.Show("Welcome to iDSTEM!");
        }
            catch (Exception ex)
        {
                MessageBox.Show(ex.Message);
            }

Answer 1

You need the command itself - you're building it later:

MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase);

Just move that higher, and then use:

cmdDataBase.Parameters.AddWithValue(...);

It's not clear why you're creating the parameter variable at all, as you're never using it.

I would actually not use AddWithValue , but instead use:

cmdDataBase.Parameters.Add("@userid", MySqlDbType.VarChar).Value = userid_txt.Text;
// etc

MySQL doesn't have a type of NVarChar , so MySqlDbType doesn't either, hence your error - I strongly suspect you just want VarChar . You don't need to specify the direction - that's implicitly "input" by default.

Additionally, you should be using using statements for your connection and command:

using (var connection = new MySqlConnection(...))
{
    using (var command = new MySqlCommand(sql, connection))
    {
        ...
    }
}