cvp-query-term-alias.php

<?php

add_filter( 'terms_clauses', 'cvp_query_term_alias', 10, 3 );

/**
 * Allow querying the term alias field.
 *
 * @param array $query_clauses
 * @param array $taxonomies
 * @param array $args
 *
 * @return array
 */
function cvp_query_term_alias( array $query_clauses, array $taxonomies, array $args ) {
	// Make sure we have the field.
	if ( ! isset( $args['alias_of'] ) ) {
		return $query_clauses;
	}

	// Massage the alias_of field into an array.
	$alias_of = is_numeric( $args['alias_of'] )
		? [ (int) $args['alias_of'] ]
		: array_map( 'absint', $args['alias_of'] );

	// If for some reason the alias field is empty, return early.
	if ( empty( $alias_of ) ) {
		return $query_clauses;
	}

	// We are going to build an array of the term groups.
	$groups = [];

	foreach ( $alias_of as $term_id ) {
		$term = get_term( $term_id );

		/**
		 * This is, admittedly, a hack.
		 *
		 * The idea here is that if someone wants aliases of a term,
		 * but the term does not have aliases, the query should
		 * actually return no results.
		 *
		 * So here, we set the group value to PHP_INT_MAX to ensure
		 * we don't return any results for this particular group.
		 *
		 * If you have passed multiple `alias_of` values, you will
		 * still correctly get results for any terms which _do_ have
		 * aliases.
		 *
		 * But if none of your terms have aliases, you'll get nothing
		 * back as it's unlikely that we will ever have a term_group
		 * with an ID equivalent to PHP_INT_MAX.
		 *
		 * Again, it's a hack. Shrug!
		 */
		if ( (int) $term->term_group === 0 ) {
			$groups[] = PHP_INT_MAX;

			continue;
		}

		// Add the term groups to our query
		$groups[] = $term->term_group;
	}

	// Get a string version of the groups.
	$groups = implode( ", ", array_unique( $groups ) );

	// Build the query.
	$query_clauses['where'] .= " AND t.term_group IN ({$groups})";

	return $query_clauses;
}