function getAllBook()
 {
     $key = 'book';
     $collection = CacheManager::get($key, TRUE);
     if ($collection) {
         return $collection;
     }
     $collection = new Collection();
     $this->connect();
     $result = $this->conn->query("CALL sp_get_all_book()");
     if ($result) {
         //$row = $result->fetch_assoc();
         while ($obj = $result->fetch_object()) {
             $book = new Book();
             $book->setBookId($obj->Book_id);
             $book->setTitle($obj->Title);
             $book->setPublisherId($obj->Publisher_id);
             $book->setIsbn($obj->Isbn);
             $book->setCategoryId($obj->Category_id);
             $book->setPublisherName($obj->Publisher_name);
             $book->setCategoryName($obj->Subject);
             $collection->addItem($book, $obj->Book_id);
         }
         $result->close();
         // for fetch_object()
     }
     //$result->free_result(); // for fetch_assoc()
     $this->close();
     CacheManager::set($key, $collection, TRUE);
     return $collection;
 }