navigation menu both submenu and parent class active

[UD2006]

I have a navigation menu with one level of submenu, and the code that I have allowes me when I click on the parent, the submenu opens (and remains open). When I click on a subitem, the page travels to that url, but the code that I have compares the document.location to the href of the menu items and display the submenu.
Now the active page is hightlighted, but the parent isn't (if the active page is a submenu).
So what I want is that when a subitem is active, also it's parent should be active, for example:

main_item_1
main_item_2
--sub_item_1
--sub_item_2

In this case when sub_item_2 is active, also main_item_2 should be.

I have tried to use parent(), parents(), but none worked the right way, or at least for me the way I want it.

So here is the code I use:

$('#topnav ul li ul.submenu li a').click(function(e){
     if ($(this).attr('class') != 'active'){
       $('#topnav ul li a').removeClass('active');
       $(this).addClass('active');
     }
   });
	   $('a').filter(function(){
			return this.href === document.location.href;
	   }).addClass('active')
	   $("ul.submenu > li > a").each(function () {
         var currentURL = decodeURIComponent(document.location.href);
         var thisURL = $(this).attr("href");
         if (currentURL.indexOf(thisURL) != -1) {
	         $(this).parents("ul.submenu").css('display', 'block');
         }
       });
       $('#topnav > ul > li > a').each(function(){
      var currURL = decodeURIComponent(document.location.href);
	  var myHref= $(this).attr('href');
      if (currURL.match(myHref)) {
			$(this).addClass('active');
                        //$('a', $('.active').parents("li:last")).addClass('active');		                   
             	        $(this).parent().find("ul.submenu").css('display', 'block');
	  }
	});

The middle group code is for the subitem, so the code to make the parent also active should be there I think.

Please help.

[UD2006]

anyone who can help me with this?