public function completed(UserInterface $user)
    {
        $queryBuilder = $this->createQueryBuilder('a');

        $queryBuilder
            ->where('a.user = :user')
            ->andWhere('a.completed = :completed');

        $queryBuilder
            ->setParameters([
                'user' => $user,
                'completed' => true
            ]);

        try
        {
            return $queryBuilder->getQuery()->getSingleResult();
        }
        catch (NoResultException $e)
        {
            return false;
        }
    }