public class SearchHistory {
  public SearchHistory(Long userId, Long groupId, String searchString) {
        this.userId = userId;
        this.groupId = groupId;
        this.searchString = searchString;
    }
  ...
  //getters + setters
  ...
  public void validate() throws InvalidParameterException{
    if (searchString == null || searchString.length() < MIN_WORD_SIZE) {
      throw new InvalidParameterException("Wrong search word min size: "+searchString);
    }

    if (searchString.length() > MAX_WORD_SIZE) {
        searchString = searchString.substring(0, MAX_WORD_SIZE - 1);
    }
}
}

@Repository
public class SearchHistorControllerImpl implements SearchHistoryController {

    @PersistenceContext(unitName = "userPU")
    private EntityManager userEm;

    @Override
    @Transactional
    public List<SearchHistory> getSearchHistories(Long userId) {
        return emptyIfNull(userEm.createNamedQuery("getSearchHistories")
                .setParameter("userId", userId)
                .getResultList());
    }

    @Override
    @Transactional
    public SearchHistory saveSearchHistory(Long userId, Long groupId, String word) throws InvalidParameterException{
        SearchHistory searchHistory = new SearchHistory(userId, groupId, word);
        searchHistory.validate(); //throws InvalidParameterException

        removeSameWord(userId, groupId, word);
        checkWordsSizeLimit(userId, groupId);

        searchHistory = userEm.merge(searchHistory);
        userEm.flush();
        return searchHistory;
    }

    private void removeSameWord(Long userId, Long groupId, String word) {
        userEm.createNamedQuery("removeSameWord")
                .setParameter("userId", userId)
                .setParameter("groupId", groupId)
                .setParameter("searchString", word)
                .executeUpdate();
    }

    private void checkWordsSizeLimit(Long userId, Long groupId){
        List<SearchHistory> searchHistoryIds = userEm.createNamedQuery("findOldSearchWordsIds")
                .setParameter("userId", userId)
                .setParameter("groupId", groupId)
                .setFirstResult(MAX_HISTORY_SIZE - 1)
                .getResultList();

        if (!searchHistoryIds.isEmpty()) {
            userEm.createNamedQuery("removeOldWords")
                    .setParameter("searchHistoryIds", searchHistoryIds)
                    .executeUpdate();
        }
    }
}

...
<query name="findOldSearchWordsIds">
    SELECT id
     FROM SearchHistory as searchHistory
     WHERE
        searchHistory.userId = :userId
        AND searchHistory.groupId = :groupId
     ORDER BY searchHistory.searchTime DESC
</query>

<query name="removeOldWords">
    DELETE FROM SearchHistory as searchHistory
    WHERE searchHistory.id in ( :searchHistoryIds )
</query>

<query name="removeSameWord">
    DELETE FROM SearchHistory as searchHistory
    WHERE
        searchHistory.searchString = :searchString
        AND searchHistory.userId = :userId
        AND searchHistory.groupId = :groupId
</query>
...

...
public void commandExecute() {
    buildSearchResult();

    if (whetherSaveRequestInHistory) {
        final String filteredString = StringUtils.removeEnd(filterString, "*");
        try {
            searchHistoryManager.saveSearchHistory(context.getUserId, groupId, filteredString);
        } catch (InvalidParameterException ipe) {
            log.info("Unable to save Search History to db: "+ ipe.getMessage());
        }
    }
}

...