سلام

یه فرم رزرو دارم که میخوام شماره میز و نام غذا بر اساس رستورانی که انتخاب میکنم نمایش داده بشه ولی هر کدی مینویسم نمیشه 

اینم کدم ممنون میشم راهنماییم کنید

 protected void DropDownList_restaurant_SelectedIndexChanged(object sender, EventArgs e)
    {
        string cs = ConfigurationManager.ConnectionStrings["cs"].ConnectionString;
        SqlConnection sqlcon = new SqlConnection(cs);
        SqlCommand command = new SqlCommand("  SELECT * FROM desk WHERE restaurant_code = @restaurant_code", sqlcon);
        command.Parameters.AddWithValue("@restaurant_code", DropDownList_restaurant.SelectedIndex);
        if (sqlcon.State != ConnectionState.Open)
        {
           sqlcon.Open();
        }  
        SqlDataReader dr = command.ExecuteReader();
        DropDownList_tablecode.DataSource = dr;
        DropDownList_tablecode.DataTextField = "desk_code";
        DropDownList_tablecode.DataValueField = "desk_code";
        DropDownList_tablecode.DataBind();
        DropDownList_tablecode.Items.Insert(0, new ListItem("انتخاب کنید"));

        if (sqlcon.State != ConnectionState.Closed)
           
        sqlcon.Close();


      
       
    }
   
    protected void DropDownList_tablecode_SelectedIndexChanged(object sender, EventArgs e)
    {
        string cs = ConfigurationManager.ConnectionStrings["cs"].ConnectionString;
        SqlConnection sqlcon = new SqlConnection(cs);
        SqlCommand command = new SqlCommand("  SELECT * FROM food WHERE restaurant_code = @restaurant_code", sqlcon);
        command.Parameters.AddWithValue("@restaurant_code", DropDownList_restaurant.SelectedIndex);
        if (sqlcon.State != ConnectionState.Open)
        {
            sqlcon.Open();
        }
        SqlDataReader dr = command.ExecuteReader();
        DropDownList_food.DataSource = dr;
        DropDownList_food.DataTextField = "food_name";
        DropDownList_food.DataValueField = "food_code";
        DropDownList_food.DataBind();
        DropDownList_food.Items.Insert(0, new ListItem("انتخاب کنید"));

        if (sqlcon.State != ConnectionState.Closed)

            sqlcon.Close();
    }