Force a user to select from JQuery UI Autocomplete and populate a hidden field after selecting

Question

I have a large HTML form that contains many fields that need an autocomplete for accounts. I tag these fields with the class AccountLookup and jQuery does the dirty work for the autocomplete:

$(".AccountLookup").autocomplete({
    source: function (request, response) {
        $.ajax({
            url: "Lookup.asmx/GetAccounts",
            data: "{ 'Search': '" + request.term + "' }",
            dataType: "json",
            type: "POST",
            contentType: "application/json; charset=utf-8",
            dataFilter: function (data) { return data; },
            success: function (data) {
                response($.map(data.d, function (item) {
                    return {
                        value: item.Value
                    }
                }))
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
                alert(textStatus);
            }
        });
    },
    minLength: 3
});

Now, when a user selects something from the autocomplete I need it to populate a hidden field just BEFORE the tagged input field; probably using something like:

$(this).prev().val(item.Key);

How do I incorporate this functionality? Also, how do I force a user to select from the auto complete? (All the values are pre-defined, the user cannot add new ones.)

EDIT: As far as I understand from inspecting the DOM, the select option is currently filling in the hidden form field.

select: function (event, ui) {
    $(this).prev().val(ui.item.key);
}

Answer 1

I know this is an old post--- but I ran into it in trying to solve a similar problem (forcing the user to select an item from the list)...

        $("#ac").autocomplete({
            source: function (req, resp) {
                   //add code here...
            },
            select: function (e, ui) {
                $(this).next().val(ui.item.id);
            },
            change: function (ev, ui) {
                if (!ui.item)
                    $(this).val("");
            }
        });

Answer 2

$(".AccountLookup").autocomplete({
   /*...*/
}).result(function(event, item) {
   $(this).prev().val(item.Key);
});

You could also use a jQuery validate to ensure that the field is populated.

Answer 3

for force selection, you can use "change" event of Autocomplete

        var availableTags = [
            "ActionScript",
            "AppleScript"
        ];
        $("#tags").autocomplete({
            source: availableTags,
            change: function (event, ui) {
                if(!ui.item){
                    //http://api.jqueryui.com/autocomplete/#event-change -
                    // The item selected from the menu, if any. Otherwise the property is null
                    //so clear the item for force selection
                    $("#tags").val("");
                }

            }

        });