gistfile1.php

<?php
class OfferFinder extends Blabla
{
	public function whereTags(array $tags)
	{
		if (count($tags) === 0) {
			return;
		}
		
		$ids = array_map(function ($tag) {
			return $tag->getId();
		}, $tags);
		
		$res = $this->connection->executeQuery(
			'select offer_id from offer_tag where tag_id in (' . implode(',', $ids) . ')'
		)->fetchAll();
		
		$offerIds = array_map(function ($row) {
			return (int) $row['offer_id'];
		}, $res);
		
		$this->qb->andWhere($this->qb->expr()->in('o.id', $offerIds));
		return $this;
	}
}