jQuery Forum

I solved it in dirty way :)
Actually I'm using local data, so i had trouble with that one first, here is the solution, who wants to use local data with ID's, and autopopulate default value based on ID in query string

1. var data = [ // array of local data
       {text:'Cat 1', aid:'1'},
2.     {text:'Cat 2', aid:'2'}
3.     // ... etc
      ];

1. $("input#cat").autocomplete(data, {
           matchContains: true,
           minChars: 0,
           max: 120,
         formatItem: function(item) {
           return item.text; // return 'Cat 1' or 'Cat 2' inside autocomplete
         }
       }).result(function(item) {
         $("#category").val(item.aid); // add ID to the hidden field which goes to DB actually
     });

Now You will need your programming language:

1. if querystring <> '' // this line is just example, not really any programming language
2. 
       $('#cat').val('Cat 1'); // also you will need to retrieve CAT name with your program. language
       $('#category').val('1'); // also you will need to retrieve CAT ID with your program. language
   
   

And thats it :)
On focus of autocomplete field, cat name doesn't disappear , id is added... etc

Hope will help someone

      $('.ui-autocomplete-input').val($('.ui-autocomplete-input').val());