Table joining using zend2 hydrate - orm

Question

I have a form to insert users to DB, which needs to update two tables # once, user table and user_role_linker table. I am using hydrator (ClassMethod) to map my entities with the relative tables. I use two seperate entities, User and UserRole. The form contains all user fields that map with User table and user role field to map with user_role_linker table. When form submitted, bind the form with the User Entity.
$user = new \ZfcUser\Entity\User();
$form = $this->getRegisterForm();
$form->setHydrator($this->getFormHydrator());
$form->bind($user);
$user = $form->getData();
Inserting is perform in two steps.
$this->getUserMapper()->insert($user);
$user_role_linker->setId($user->getId());
$user_role_linker->setRoleId($data['user_role']);
$this->getUserRoleLinkMapper()->insert($user_role_linker);
First insert the user and return the user_id, then set user_id and user_role in UserRole entity and insert to table.
But now the problem is to fetch two table to one object or one array. I may need to perform a table join to get the solution. But there is no way I could find to join tables with using ClassMethod hydrator.
Please help me to accomplish this.
UserHydrator class
namespace ZfcUser\Mapper;
use Zend\Stdlib\Hydrator\ClassMethods;
use ZfcUser\Entity\UserInterface as UserEntityInterface;
class UserHydrator extends ClassMethods
{
/**
* Extract values from an object
*
* #param object $object
* #return array
* #throws Exception\InvalidArgumentException
*/
public function extract($object)
{
if (!$object instanceof UserEntityInterface) {
throw new Exception\InvalidArgumentException('$object must be an instance of ZfcUser\Entity\UserInterface');
}
/* #var $object UserInterface*/
$data = parent::extract($object);
$data = $this->mapField('id', 'user_id', $data);
//$data = $this->mapField('id', 'username', $data);
return $data;
}
/**
* Hydrate $object with the provided $data.
*
* #param array $data
* #param object $object
* #return UserInterface
* #throws Exception\InvalidArgumentException
*/
public function hydrate(array $data, $object)
{
if (!$object instanceof UserEntityInterface) {
throw new Exception\InvalidArgumentException('$object must be an instance of ZfcUser\Entity\UserInterface');
}
$data = $this->mapField('user_id', 'id', $data);
return parent::hydrate($data, $object);
}
protected function mapField($keyFrom, $keyTo, array $array)
{
$array[$keyTo] = $array[$keyFrom];
unset($array[$keyFrom]);
return $array;
}
}