/// <summary> /// The button that adds the book and check all the fields. /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void btn_AddBook_Click(object sender, EventArgs e) { var author = AS.All().Where(a => a.Name == txt_Author.Text.Trim()).FirstOrDefault(); if (txt_ISBN.Text.Trim() == "" || txt_Title.Text.Trim() == "" || txt_Description.Text.Trim() == "" || txt_Author.Text.Trim() == "") { MessageBox.Show("Please enter all the fields."); } else if (BS.BookAlreadyExists(txt_ISBN.Text.Trim())) { MessageBox.Show("This Book already exists"); } else { if (author != null) { Book book = new Book() { ISBN = txt_ISBN.Text.Trim(), Title = txt_Title.Text.Trim(), Description = txt_Description.Text.Trim(), Author = author }; try { BS.Add(book); } catch (ArgumentNullException ex) { MessageBox.Show(ex.Message); } } else { Author author2 = new Author() { Name = txt_Author.Text.Trim() }; Book book = new Book() { ISBN = txt_ISBN.Text.Trim(), Title = txt_Title.Text.Trim(), Description = txt_Description.Text.Trim(), Author = author2 }; AS.Add(author2); BS.Add(book); this.Close(); } } }