Drupal Form autocomplete - drupal

Question

I wanted to have a textfield in a form that autocompletes from the database. I have been reading the tutorials and trying to get it to work but thus far not much luck. I am farely new to Drupal so I'm mostly unsure what I am doing xD
My code thus far:
function my_module_menu() {
$items = array();
$items['my_module/form'] = array(
'title' => t('Add List'),
'page callback' => 'my_module_form',
'access arguments' => array('access content'),
'description' => t('My form'),
'type' => MENU_CALLBACK,
);
// path with autocomplete function for casters
$items['caster/autocomplete'] = array(
'title' => t('Autocomplete for casters'),
'page callback' => '_caster_autocomplete',
'access arguments' => array('use autocomplete'),
'type' => MENU_CALLBACK
);
return $items;
}
function my_module_form() {
return drupal_get_form('my_module_my_form');
}
function _caster_autocomplete($string) {
$matches = array();
$results = db_select('warnoun', 'w')
->fields('w', array('full_name'))
->condition('full_name', '%' . db_like($string) . '%', 'LIKE')
->execute();
// save the query to matches
foreach ($results as $result) {
$matches[$result->full_name] = check_plain($result->full_name);
}
// Return the result to the form in json
drupal_json_output($matches);
}
function my_module_my_form($form_state) {
$form['points'] = array(
'#type' => 'select',
'#title' => t('Points'),
'#required' => TRUE, // Added
'#options' => array(
0 => t('15'),
1 => t('25'),
2 => t('35'),
3 => t('50'),
),
);
$form['caster'] = array(
'#type' => 'textfield',
'#title' => t('Caster'),
'#maxlength' => 50,
'#autocomplete_path' => 'caster/autocomplete',
'#required' => TRUE,
);
$entries = db_query('SELECT id, short_name FROM factions ORDER BY id ASC');
$options = array();
foreach ($entries as $entry){
$options[$entry->id] = t($entry->short_name);
}
$form['faction'] = array(
'#type' => 'select',
'#title' => t('Faction'),
'#options' => $options,
);
// Simple Submit Button
$form['submit'] = array(
'#type' => 'submit',
'#value' => 'Submit',
'#required' => TRUE, // Added
);
return $form;
}
So basically there is a table called warnoun with a column full_name and it's with that content that I want to autocomplete the textfield caster.
Any idea what I'm missing/doing wrong?
Cheers