A simple example of a function that gathers data from a doctrine and makes use of the join. Nothing special just good for reference

DoctrineDQLExample

  /**
	 * Function to select particpants by their particiation 
	 * 
	 * @param integer $statusId Status id of partipation 
	 * @param integer $value    Value for query
	 * @param string  $operator Operator for claus  opions: moreThan, lessThan, atLeast, equals
	 * 
	 * @return array
	 */
	public function selectUsersByParticipation($statusId, $value, $operator)
	{
		$parameters = array(
				'attendanceStatusId' => $statusId,
				'value' => $value
		);
		
		switch ($operator) {
			case "moreThan":
				$operator = '>';
				break;
			case "lessThan":
				$operator = '<';
				break;
			case "atLeast":
				$operator = '>=';
				break;
			case "equals":
				$operator = '=';
				break;
		}
		
		// The HIDDEN keyword takes the value out of the results
		// This which makes for easier use of the results (unless you need to the count in the results)
		$dql = 'SELECT p, COUNT(t.participantId) HIDDEN number
				FROM Library\Entity\Participant p
				LEFT JOIN p.surveyParticipants t
				WHERE t.attendanceStatusId = :attendanceStatusId
				GROUP BY t.participantId
				HAVING number '.$operator.' :value';
			
		
		$query = $this->_em->createQuery($dql)->setParameters($parameters);
	
		$result = $query->getResult();
	
		return $result;
	}