private async void AddButton_Click(object sender, EventArgs e)
        {
            AddEditClient aec = new AddEditClient();

            aec.ServiceCB.DataSource    = services;
            aec.ServiceCB.ValueMember   = "Id";
            aec.ServiceCB.DisplayMember = "Name";


            DialogResult result = aec.ShowDialog(this);

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

            Client client = new Client()
            {
                Firstname = aec.FirstnameTB.Text,
                Surname   = aec.SecondnameTB.Text,
                Lastname  = aec.LastnameTB.Text,
                Number    = (int)aec.NumberTB.Value,
                OrderTime = aec.dataTB.Value,
                Service   = (Service)aec.ServiceCB.SelectedItem
            };

            context.Clients.Add(client);
            await context.SaveChangesAsync();

            MessageBox.Show("Клиент был добавлен");
            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;
                }

                Client client = await context.Clients.FindAsync(id);

                AddEditClient aec = new AddEditClient();

                aec.FirstnameTB.Text       = client.Firstname;
                aec.SecondnameTB.Text      = client.Surname;
                aec.LastnameTB.Text        = client.Lastname;
                aec.NumberTB.Value         = (decimal)client.Number;
                aec.dataTB.Value           = client.OrderTime;
                aec.ServiceCB.SelectedItem = client.Service;

                aec.ServiceCB.DataSource    = services;
                aec.ServiceCB.ValueMember   = "Id";
                aec.ServiceCB.DisplayMember = "Name";

                DialogResult result = aec.ShowDialog(this);

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

                client.Firstname = aec.FirstnameTB.Text;
                client.Surname   = aec.SecondnameTB.Text;
                client.Lastname  = aec.LastnameTB.Text;
                client.Number    = (int)aec.NumberTB.Value;
                client.OrderTime = aec.dataTB.Value;;
                client.Service   = (Service)aec.ServiceCB.SelectedItem;

                await context.SaveChangesAsync();

                MessageBox.Show("Клиент был изменен");
                dataGridView1.Refresh();
            }
        }