getting selected item's ID value in autocomplete form

In case anyone else decides they want this kind of functionality I found a patch and some instructions on how to make this work. I haven't tried it yet so hopefully it will work for me.

http://drupal.org/node/322383

I just don't know enough about Javascript to get this to work with that approach. I'm very green with coding in general but I did come up with an alternative hack. These are the steps in case anyone not familiar with Javascript wants to do something similar.

In the autocomplete function you can format the pop up values one way and what's actually put into the field can be formatted differently. Below is where I declare what these values should be for my autocomplete field inside the autocomplete callback.

$matches[$city->cityName . '|' . cityID] = $city->cityName;

When the user types into the autocomplete field only the matching cityName values pop up. This is the value on the right of the = sign.

After they make a selection the autocomplete form field is populated with the concatenated value on the left of the = sign. The resulting string is "cityName|cityID" (an actual value would be something like "New York|123545"). This string is ugly but it only appears on the field for a split second and is replaced via ahah (I'm using the AHAH helper module) by the city name alone ("New York" in this case).

The cityID value is then put into a hidden form element so I can use it on submit. Since I already have these values in my db the cityID value is all I need, the city's name is just for the user's benefit. This is working great so far for me and here's how it works:

In my form function I use the explode() function on the "cityName|cityID' string using "|" as the separator. This changes the string to an array with cityName in position 0 and cityID in position 1. Since my form element is ahah enabled the function is run as soon as the value is put on the field ('event' => 'blur' inside the '#ahah' array) which is why this ugly string only appears for a split second. See below for part of code where it all happens:

<?php // Do not include php tags
// Pulls autocomplete field value "cityName|cityID" from $form_state array.
$city_field_value = $form_state['values']['city'];

// Checks if autocomplete field's current value has already been exploded by looking
// for the "|" separator in the string. If the separator doesn't exist the string was already
// exploded so the explode() function is skipped
$needs_explode = strpos($city_field_value, "|");
// === used because explode function confuses position 0 in array with FALSE
// when there's only one value(or so I've read).
if ($needs_explode === FALSE) {
   // $selected_city_name is my autocomplete field's default value.
   $selected_city_name = $city_field_value;
}
// After explode() is exectued I put the selected cityID value into $select_city_id
// which is the default value of my hidden field. This is what I needed!!!!!
// The ugly string "cityName|cityID" is replaced by "cityName" since
// $select_city_name is the autocomplete field's default value.
else {
       $city_field_exploded = explode('|', $city field value);
       $selected_city_id = $city_field_exploded[1];
       $selected_city_name = $city_field_exploded[0];
}

// Autocomplete form field
$form['my_form']['city'] = array(
   '#type'  => 'textfield',
   '#title' => 'city',
   '#value' => $selected_city_name,
   '#autocomplete_path' => 'my_path/autocomplete',
   '#ahah' => array(
        'event' => 'blur',
        // Using the AHAH helper module to simplify ahah implementation
        'path' => ahah_helper_path(array('globalize')),
        'wrapper' => 'myform-wrapper',
        'effect' => 'fade,
   ),
);

// This is the field that really matters to me.
$form['my_form']['cityid'] = array(
   '#type'  => 'hidden',
   '#value' => $selected_city_id,
   ),
);
?>

Again, I'm fairly new to coding but this worked great for me. I'm sure someone with more experience has an even better way or can improve on this approach. If this helps anyone I'll be glad I could finally give back to the community after all the help I've received to get me to this point.