c# – 如何从web.config添加和访问连接字符串

这是我的代码示例,在单击按钮以连接到数据库之后运行.

protected void Button2_Click(object sender,EventArgs e)
    {
        String a = DropDownList1.SelectedItem.Value;
        String b = DropDownList3.SelectedItem.Value.PadLeft(3,'0');      
        String c = TextBox2.Text.PadLeft(5,'0').ToString();
        String d = TextBox3.Text.ToString();
        String digit = a+ b  + c + d;
        try
        {
         myConn = new OdbcConnection("Driver={MySQL ODBC 3.51 Driver};Server=localhost;Database=testcase;User=root;Password=root;Option=3;");
         myConn.Open();
            //**
            string sql = "select * from testcase.main where reg_no =?";            
            //**
            OdbcCommand cmd = new OdbcCommand(sql,myConn);            
            //**
            cmd.Parameters.AddWithValue("?",digit);
            MyReader = cmd.ExecuteReader();
            //**
            while (MyReader.Read())
            {
                String f = MyReader["pet_name"].ToString();
                String g = MyReader["res_name"].ToString();

                Label9.Visible = true;
                Label9.Text = f;

                Label10.Visible = true;
                Label10.Text = "VS";

                //Label11.Visible = true;
                Label11.Text = g;

            }

            MyReader.Close();
        }
        catch (Exception e1)
        {
            Response.Write(e1.ToString());
        }
        finally
        {
            if (MyReader != null && !MyReader.IsClosed)
            {
                MyReader.Close();   
            }

            if (myConn != null && myConn.State == ConnectionState.Open)
            {
                myConn.Close();
            }
        }