private void SelectCategoriesButton_Click(object sender, EventArgs e)
{
var categories = CategoryCheckedListBox.CheckedCategoriesList().Select(category => (int?)category.CategoryID);
var ops = new DataOperations();
var data = ops.ProductsByCategories(categories.ToList()).ToList();
ProductDataGridView.DataSource = data;
ProductDataGridView.ExpandColumns();
}
