private void btnAdd_Click(object sender, EventArgs e)
        {
            ProductController controller = new ProductController();

            SalesProductModel model = new SalesProductModel();
            ProductDBModel    db    = new ProductDBModel();

            model.Name         = txtProductName.Text;
            model.Serialnumber = Convert.ToInt32(txtSerialnumber.Text);
            model.Quantity     = Convert.ToInt32(txtQuantity.Text);
            model.Unitprice    = Convert.ToInt32(txtPricePerUnit.Text);
            model.Description  = txtDescription.Text;
            model.DateImport   = dtpDateImport.Text;

            //true mean visible, have to use another
            if (db.CheckVisibleName(model.Name))
            {
                MessageBox.Show("Name visible");
            }
            else
            {
                if (db.CheckVisibleSerialnumber(model.Serialnumber.ToString()))
                {
                    MessageBox.Show("Serialnumber visible");
                }
                else
                {
                    if (controller.AddProduct(model))
                    {
                        MessageBox.Show("insert successful");
                    }
                    else
                    {
                        MessageBox.Show("insert invalide");
                    }
                }
            }
        }