Omeka function to return Tags associated with Items in a given Collection.

get_tags_for_items_in_collection.php

<?php
/**
 * Return Tags associated with Items in a given Collection.
 *
 * @param Collection
 * @return array Tags.
 */
function get_tags_for_items_in_collection($collection = null) {

    // If collection is null, get the current collection.
    if (!$collection) {
        $collection = get_current_collection();
    }

    // Get the database.
    $db = get_db();

    // Get the Tag table.
    $table = $db->getTable('Tag');

    // Build the select query.
    $select = $table->getSelectForFindBy();   

    // Join to the Item table where the collection_id is equal to the ID of our Collection.
    if ($collection) {
        $table->filterByTagType($select, 'Item');
        $select->where('i.collection_id = ?', $collection->id);
    }

    // Fetch some tags with our select.
    $tags = $table->fetchObjects($select);

    return $tags;
}