private async void AddButton_Click(object sender, EventArgs e)
        {
            AddEditSeller addSeller = new AddEditSeller();

            addSeller.ShopCB.DataSource    = shops;
            addSeller.ShopCB.ValueMember   = "Id";
            addSeller.ShopCB.DisplayMember = "Name";

            DialogResult result = addSeller.ShowDialog(this);

            if (result == DialogResult.Cancel)
            {
                return;
            }

            Seller seller = new Seller()
            {
                Shop            = (Shop)addSeller.ShopCB.SelectedItem,
                Firstname       = addSeller.FirstNameTB.Text,
                Surname         = addSeller.SurnameTB.Text,
                Address         = addSeller.AddressTB.Text,
                DataBirth       = addSeller.dateOfBirthBox.Value,
                NumberPassport  = (int)addSeller.NumberPassp.Value,
                NameGetPassport = addSeller.NameGetPasppBox.Text,
                DataGetPassport = addSeller.DateGetPassportBox.Value,
                Department      = addSeller.DepartmentTB.Text
            };

            context.Selleres.Add(seller);
            await context.SaveChangesAsync();

            MessageBox.Show("Seller was added");
            dataGridView1.Refresh();
        }
        private async void EditButton_Click(object sender, EventArgs e)
        {
            if (dataGridView1.SelectedRows.Count > 0)
            {
                int  index     = dataGridView1.SelectedRows[0].Index;
                int  id        = 0;
                bool converted = Int32.TryParse(dataGridView1[0, index].Value.ToString(), out id);
                if (converted == false)
                {
                    return;
                }

                Seller seller = await context.Selleres.FindAsync(id);

                AddEditSeller addSeller = new AddEditSeller();

                addSeller.ShopCB.DataSource    = shops;
                addSeller.ShopCB.ValueMember   = "Id";
                addSeller.ShopCB.DisplayMember = "Name";

                addSeller.ShopCB.SelectedItem      = seller.Shop;
                addSeller.FirstNameTB.Text         = seller.Firstname;
                addSeller.SurnameTB.Text           = seller.Surname;
                addSeller.AddressTB.Text           = seller.Address;
                addSeller.dateOfBirthBox.Value     = seller.DataBirth;
                addSeller.NumberPassp.Value        = seller.NumberPassport;
                addSeller.NameGetPasppBox.Text     = seller.NameGetPassport;
                addSeller.DateGetPassportBox.Value = seller.DataGetPassport;
                addSeller.DepartmentTB.Text        = seller.Department;

                DialogResult result = addSeller.ShowDialog(this);

                if (result == DialogResult.Cancel)
                {
                    return;
                }

                seller.Shop            = (Shop)addSeller.ShopCB.SelectedItem;
                seller.Firstname       = addSeller.FirstNameTB.Text;
                seller.Surname         = addSeller.SurnameTB.Text;
                seller.Address         = addSeller.AddressTB.Text;
                seller.DataBirth       = addSeller.dateOfBirthBox.Value;
                seller.NumberPassport  = (int)addSeller.NumberPassp.Value;
                seller.NameGetPassport = addSeller.NameGetPasppBox.Text;
                seller.DataGetPassport = addSeller.DateGetPassportBox.Value;
                seller.Department      = addSeller.DepartmentTB.Text;

                await context.SaveChangesAsync();

                MessageBox.Show("Seller was updated");
                dataGridView1.Refresh();
            }
        }