public void PopulateAssignedCategoryData(Moldovan_Sonia_Lab8Context context,
                                                 Book book)
        {
            var allCategories  = context.Category;
            var bookCategories = new HashSet <int>(
                book.BookCategories.Select(c => c.BookID));

            AssignedCategoryDataList = new List <AssignedCategoryData>();
            foreach (var cat in allCategories)
            {
                AssignedCategoryDataList.Add(new AssignedCategoryData
                {
                    CategoryID = cat.ID,
                    Name       = cat.CategoryName,
                    Assigned   = bookCategories.Contains(cat.ID)
                });
            }
        }
        public void UpdateBookCategories(Moldovan_Sonia_Lab8Context context,
                                         string[] selectedCategories, Book bookToUpdate)
        {
            if (selectedCategories == null)
            {
                bookToUpdate.BookCategories = new List <BookCategory>();
                return;
            }
            var selectedCategoriesHS = new HashSet <string>(selectedCategories);
            var bookCategories       = new HashSet <int>
                                           (bookToUpdate.BookCategories.Select(c => c.Category.ID));

            foreach (var cat in context.Category)
            {
                if (selectedCategoriesHS.Contains(cat.ID.ToString()))
                {
                    if (!bookCategories.Contains(cat.ID))
                    {
                        bookToUpdate.BookCategories.Add(
                            new BookCategory
                        {
                            BookID     = bookToUpdate.ID,
                            CategoryID = cat.ID
                        });
                    }
                }
                else
                {
                    if (bookCategories.Contains(cat.ID))
                    {
                        BookCategory courseToRemove
                            = bookToUpdate
                              .BookCategories
                              .SingleOrDefault(i => i.CategoryID == cat.ID);
                        context.Remove(courseToRemove);
                    }
                }
            }
        }