Here's another solution using a simple lightweight db_select query on taxonomy_term_data.
It provides two functions, one to get the next term, and one to get the previous.
The idea is to select the next ( or previous ) term in the same vocabulary with a weight greater ( or less than ) than current term, ordered by weight and limited to one result. A static cache is used so query only performed once per page load.
/**
* Return next term id by weight
* @param $term taxonomy term object
* @return int term id or FALSE if none exists
*/
function EXAMPLE_next_term($term) {
// Use static cache
$next = &drupal_static(__FUNCTION__ . '_' . $term->tid, FALSE);
if(!$next){
$next = db_select('taxonomy_term_data', 'td')
->fields('td', array('tid'))
->condition('weight', $term->weight, '>')
->condition('vid', $term->vid)
->orderBy('weight')
->range(0,1)
->execute()
->fetchField();
}
return $next;
}
/**
* Return previous term id by weight
* @param $term taxonomy term object
* @return int term id or FALSE if none exists
*/
function EXAMPLE_previous_term($term) {
// Use static cache
$previous = &drupal_static(__FUNCTION__ . '_' . $term->tid, FALSE);
if(!$previous){
$previous = db_select('taxonomy_term_data', 'td')
->fields('td', array('tid'))
->condition('weight', $term->weight, '<')
->condition('vid', $term->vid)
->orderBy('weight')
->range(0,1)
->execute()
->fetchField();
}
return $previous;
}
Example usage:
if($tid = EXAMPLE_next_term($term)){
$next_term = taxonomy_term_load($tid); // Load full term
$link = l($next_term->name, 'taxonomy/term/'.$next_term->tid);
}