DropDownList not populating Textbox. Why?

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I have a code to populate a textbox depending on the ddl value. Why is my code not working? What did I do wrong?

C#

protected void DropDownListLongName_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection con2 = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["HotConnectionString"].ConnectionString);
            con2.Open();

            SqlCommand scmd = new SqlCommand("Select User_ID, LongName from Table99 where LongName = '" + DropDownListLongName + "'", con2);

            SqlDataReader dr = scmd.ExecuteReader();

            if (dr.Read())

            {
                TextBoxUser_ID.Text = dr["User_ID"].ToString();
            }

            dr.Close();
            con2.Close();
        }
    }
}

Posted 19-May-15 4:03am

Computer Wiz99

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Richard Deeming 19-May-15 10:21am

Your code is vulnerable to SQL Injection[^].

NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.

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Richard Deeming · Answer 1 · 2015-05-19T04:26:00

Start by fixing the SQL Injection[^] vulnerability in your code.

That will then tell you that you're trying to pass the DropDownList control to the query, instead of passing its selected value.

Also, you should wrap all objects that implement IDisposable in a using block.

And to retrieve a single value from the query, there's no need for a DataReader - just call ExecuteScalar.

C#

protected void DropDownListLongName_SelectedIndexChanged(object sender, EventArgs e)
{
    using (SqlConnection con2 = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["HotConnectionString"].ConnectionString))
    using (SqlCommand scmd = new SqlCommand("Select User_ID from Table99 where LongName = @LongName", con2))
    {
        scmd.Parameters.AddWithValue("@LongName", DropDownListLongName.SelectedValue);

        con2.Open();
        TextBoxUser_ID.Text = Convert.ToString(smcd.ExecuteScalar());
    }
}