public Task <IEnumerable <Article> > DoSearch(SearchRequest request)
        {
            switch (request.SearchMode)
            {
            case SearchMode.Signature:
            {
                return(signatureService.DoSearch(request.SearchString));
            }
            break;

            case SearchMode.Trie:
            {
                return(trieSearchService.DoSearch(request.SearchString));
            }
            break;

            default:
            {
                return(searchService.DoSearch(request.SearchString));
            }
            break;
            }
        }