public function getUsers(Criteria $criteria = null, ConnectionInterface $con = null)
    {
        $partial = $this->collUsersPartial && !$this->isNew();
        if (null === $this->collUsers || null !== $criteria || $partial) {
            if ($this->isNew()) {
                // return empty collection
                if (null === $this->collUsers) {
                    $this->initUsers();
                }
            } else {

                $query = ChildUserQuery::create(null, $criteria)
                    ->filterByRole($this);
                $collUsers = $query->find($con);
                if (null !== $criteria) {
                    return $collUsers;
                }

                if ($partial && $this->collUsers) {
                    //make sure that already added objects gets added to the list of the database.
                    foreach ($this->collUsers as $obj) {
                        if (!$collUsers->contains($obj)) {
                            $collUsers[] = $obj;
                        }
                    }
                }

                $this->collUsers = $collUsers;
                $this->collUsersPartial = false;
            }
        }

        return $this->collUsers;
    }