Inheritance: IThemeRepository
 public ArticleController()
 {
     authorRepository = new AuthorRepository(db);
     themeRepository = new ThemeRepository(db);
 }
 public AuthorController()
 {
     themeRepository = new ThemeRepository(db);
 }
 public BookController()
 {
     authorRepository = new AuthorRepository(db);
     themeRepository = new ThemeRepository(db);
 }