private void btnAddBook_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtNameBook.Text))
            {
                MessageBox.Show("Kitab adi daxil edin");
                return;
            }
            if (string.IsNullOrEmpty(cmbAuthorBook.Text))
            {
                MessageBox.Show("Yazici secin");
                return;
            }
            if (string.IsNullOrEmpty(cmbJanraBook.Text))
            {
                MessageBox.Show("Janr secin");
                return;
            }
            if (string.IsNullOrEmpty(dtpDateBook.Text))
            {
                MessageBox.Show("Tarix secin");
                return;
            }
            if (txtPriceBook.Text == "0")
            {
                MessageBox.Show("Kitab Qiymetini daxil edin");
                return;
            }
            if (txtQuantityBook.Text == "0")
            {
                MessageBox.Show("Kitab sayi daxil edin");
                return;
            }
            BookJanra  janraid  = _context.BookJanras.FirstOrDefault(u => u.Name == cmbJanraBook.Text);
            BookAuthor authorId = _context.BookAuthors.FirstOrDefault(u => u.Name == cmbAuthorBook.Text);
            Book       book     = new Book()
            {
                Name              = txtNameBook.Text,
                AuthorId          = Convert.ToInt32(authorId.Id),
                JanraId           = Convert.ToInt32(janraid.Id),
                PurchaseDate      = dtpDateBook.Value,
                Prise             = txtPriceBook.Value,
                Quantity          = Convert.ToInt32(txtQuantityBook.Value),
                AvaliableQuantity = Convert.ToInt32(txtQuantityBook.Value)
            };

            _context.Books.Add(book);
            _context.SaveChanges();
            MessageBox.Show("Kitab Elave olundu");
        }
        private void btnJanraAdd_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtJanra.Text))
            {
                MessageBox.Show("Janr Elave Edin");
                return;
            }
            BookJanra bookJanra = new BookJanra
            {
                Name = txtJanra.Text
            };

            _context.BookJanras.Add(bookJanra);
            _context.SaveChanges();
            dgvJanras.Rows.Clear();
            FillJanras();
        }