Find entity by exact matching in collection

Use HAVING with CASE to count matched userId and check equal with searched userIds count.

@Query(value = "SELECT c FROM Conversation c LEFT JOIN c.usersIds cu GROUP BY c "
           + "HAVING SUM(CASE WHEN cu IN (:userIds) THEN 1 ELSE -1 END) = :userIdsCount")
List<Conversation> findByUserIds(@Param("userIds") List<String> userIds,
                                 @Param("userIdsCount") Integer userIdsCount);