void prepareCarForEdit(Guid id)
        {
            carToEdit = carshop_db.Instance.Cars.Single(x => x.id.Equals(id));

            textBoxCount.Text = carToEdit.quantity.ToString();
            textBoxCreationDate.Text = carToEdit.creationDate.ToString();
            textBoxMarka.Text = carToEdit.marka;
            textBoxModel.Text = carToEdit.model;
            textBoxPrice.Text = carToEdit.price.ToString();
            richTextBoxDescription.Text = carToEdit.description;
            comboBoxCategory.SelectedIndex = comboBoxCategory.FindStringExact(carToEdit.Category.name);

            edit = true;
        }
 private void buttonCancelEdit_Click(object sender, EventArgs e)
 {
     edit = false;
     carToEdit = null;
     clear();
     buttonCancelEdit.Visible = false;
 }