c# multiple dropdowns

Question

Table i need to sort

So i got this 5 drop downs i need to use for sorting output from sql

Now i use

DropDownList_Instruktorer.Items.Insert(0, new ListItem("Vælg Instruktør", "*"));

For the Default Value, and i was thinking this will do the job. But

cmd.Parameters.addwithvalue

enter the value into value obviously instead of use * to show all results like it normally does in sql

SqlCommand cmd = new SqlCommand(@"SELECT * FROM Hold 
                                            INNER JOIN Instruktorer
                                            ON instruktor_id = fk_in_id
                                            INNER JOIN Stilarter
                                            ON stilart_id = fk_st_id
                                            INNER JOIN  Aldersgruppe
                                            ON aldersgruppe_id = fk_ag_id
                                            INNER JOIN Niveauer
                                            ON niveau_id = fk_ni_id
                                            INNER JOIN Tider
                                            ON tid_id = fk_ht_id
                                            WHERE fk_in_id = @Instruktor AND
                                            fk_st_id = @Stilart AND
                                            fk_ag_id = @Aldersgruppe AND
                                            fk_ni_id = @Niveau AND
                                            fk_ht_id = @Tid", conn);
    cmd.Parameters.AddWithValue("@Instruktor", DropDownList_Instruktorer.SelectedValue);
    cmd.Parameters.AddWithValue("@Stilart", DropDownList_Stilart.SelectedValue);
    cmd.Parameters.AddWithValue("@Aldersgruppe", DropDownList_Aldersgrupper.SelectedValue);
    cmd.Parameters.AddWithValue("@Niveau", DropDownList_Niveauer.SelectedValue);
    cmd.Parameters.AddWithValue("@Tid", DropDownList_Tider.SelectedValue);

Here is my sql, Any idea how i can i get it to work without writing 25 if statements?

Answer 1

Why not use a string in place of the AddWithValue, eg:

string instructorStr = "";
string stilartStr = "";
...
if (DropDownList_Instruktorer.SelectedValue != "*")
{
    instructorStr = "fk_in_id = " + DropDownList_Instruktorer.SelectedValue + " AND";
}
if (DropDownList_Stilart.SelectedValue != "*")
{
    stilartStr = "fk_st_id = " + DropDownList_Stilart.SelectedValue + " AND";
}
...

SqlCommand cmd = new SqlCommand(@"SELECT * FROM Hold 
    INNER JOIN Instruktorer
    ON instruktor_id = fk_in_id
    INNER JOIN Stilarter
    ON stilart_id = fk_st_id
    INNER JOIN  Aldersgruppe
    ON aldersgruppe_id = fk_ag_id
    INNER JOIN Niveauer
    ON niveau_id = fk_ni_id
    INNER JOIN Tider
    ON tid_id = fk_ht_id
    WHERE " + 
    instructorStr + 
    stilartStr +
    ...
    + " 1 = 1", conn);

Then you have the option to do all sorts of stuff with the individual variables, including ORDER BY

Using Stringbuilder would be cleaner but it's easier to show it this way.