Error in SQL parameter string does not contain definition.

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Hi I have an error"'object' does not contain a definition for 'AddWithValue' and no accessible extension method 'AddWithValue' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)" where did I do wrong

What I have tried:

C#

private void btnadd_Click(object sender, EventArgs e)
     {
         try
         {
             con.Close();
             cmd = new MySqlCommand("SELECT * FROM account where code = '" + txtcode.Text + "' OR description = '" + txtaccountname.Text + "'", con.con);
             con.Open();
             reader = cmd.ExecuteReader();
             if (!reader.Read())
             {
                 //insert tenant details
                 con.Close();
                 cmd = new MySqlCommand("INSERT INTO `account`(`Type`, `Code`, `Description`) VALUES (@type,@code,@description);", con.con);
                               cmd.Parameters.AddWithValue("@type", txttype.SelectedValue);
                 cmd.Parameters.AddWithValue("@code", txtcode.Text);
                 cmd.Parameters.AddWithValue("@description", txtaccountname.Text);

                 con.Open();
                 reader = cmd.ExecuteReader();

Posted 9-Oct-22 15:31pm

Marc Chester Ferrer

Updated 9-Oct-22 18:26pm

v2

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OriginalGriff · Accepted Answer · 2022-10-09T18:26:00

First off, never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?

You already know how to use parameters so why expose your DB to just anyone?

But to fix the problem you have found, we';d need to know exactly which line it complains about - because I don't think it's in that code fragment!
Double click the error message in Visual Studio, and it'll take you directly to it.