3Layer C# asp.net: insert dropdownlist selected text and value

Question

I have a 3 Layer asp.net c# code. My BL:

    public DataTable ddl()
    {
        base.Link();
        string Query = "SELECT [nam], [idZone] FROM [zones] ORDER BY idZone";
        DataTable Output_Q = base.SelectDataText(Query);
        base.UnLink();
        return Output_Q;
    }
    public void insert()
    {
        base.Link();
        string Query = "INSERT INTO students (fnam, lnam, cod, idZone) VALUES ( '{0}', '{1}', '{2}', {3} )";
        Query = string.Format(Query, fnam, lnam, cod, idZone);
        base.commanddatatext(Query);
        base.UnLink();

My Code:

    page_load:
    BL_students_new F = new BL_students_new();
    DropDownList1.Items.Clear();
    DropDownList1.DataSource = F.ddl();
    DropDownList1.DataTextField = "nam";
    DropDownList1.DataValueField = "idZone";
    DropDownList1.DataBind();

        btn_insert:
        BL_students_new F = new BL_students_new();
        F.fnam = TextBox1.Text.Trim();
        F.lnam = TextBox2.Text.Trim();
        F.cod = TextBox3.Text.Trim();
        F.idZone = Convert.ToInt32(DropDownList1.SelectedItem.Value);
        F.insert();

it saves every things but dropdownlist value. note that my ddl has text and int value and i need the value to be saved. but it fails. (My DA is OK too.)

Answer 1

From your comment above:

populating ddl is in page_load and inserting is in btn_insert

Page_Load happens before btn_Insert. This happens every time the page is requested, regardless of whether it's a "post back" or not. (After all, the page has to load into a usable state before it can even know the nature of the HTTP request.)

So what's happening is the following:

1. Bind the DropDownList options
2. Show the page to the user
3. User selects an option and submits
4. Re-bind the DropDownList options, losing whatever the user selected
5. Insert to database

A simple way to address this in WebForms is to wrap your DropDownList binding logic in a condition on IsPostBack. Something like this:

// in Page_Load:
if (!IsPostBack)
{
    BL_students_new F = new BL_students_new();
    DropDownList1.Items.Clear();
    DropDownList1.DataSource = F.ddl();
    DropDownList1.DataTextField = "nam";
    DropDownList1.DataValueField = "idZone";
    DropDownList1.DataBind();
}

That way you're only populating the DropDownList when the page is initially requested, not when the user is submitting the form.