public Publisher FindById(Guid key)
        {
            var epublisher = _publisherContext.GetItemById(Convert.ToString(key));
            var publisher  = PublisherMapping.MapToPublisher(epublisher);

            epublisher.BookIds.ToList().ForEach((bkId) => {
                var bk = _bookContext.GetItemById(bkId);
                publisher.Books.Add(new Book()
                {
                    BookId = Guid.Parse(bk.Id), title = bk.Title
                });
            });
            return(publisher);
        }
        public IList <Publisher> FindAll()
        {
            var _publishers = _publisherContext.GetItems();

            var publishers = new List <Publisher>();

            var books = _bookContext.GetItems();

            _publishers.ForEach((currentPublisher) => {
                var pub    = PublisherMapping.MapToPublisher(currentPublisher);
                var ebooks = books.FindAll(bk => Guid.Parse(bk.PublisherId) == pub.EntityIdentityKey);
                if (ebooks != null && ebooks.Count() > 0)
                {
                    ebooks.ForEach((bk) => {
                        pub.Books.Add(new Book()
                        {
                            BookId = Guid.Parse(bk.Id), title = bk.Title
                        });
                    });
                }
                publishers.Add(pub);
            });
            return(publishers.ToList());
        }