public ViewResult Archive(ArchiveFilter filter = ArchiveFilter.Alphabet)
        {
            ArchiveArticlesViewModel model = new ArchiveArticlesViewModel(null, null)
            {
                Filter = filter,
            };

            List <ArticleTitle> articles = articleRepository.GetArticlesTitles();

            model.ArticlesGroups = ArticleService.GroupArticles(articles, filter);

            return(View(model));
        }