gistfile1.txt

in a method in a Content Handler:

my $cart = WebGUI::Shop->Cart->newBySession($session);
my $asset_id = $session->db->quickScalar("select assetId from sku where sku = ?", [ $session->request->param('sku')) ]);
my $product;
if( $asset_id ) {
    $product = WebGUI::Asset::Sku::Product->newById($session, $asset_id);
} else {
    $product = WebGUI::Asset::Sku::Product->new($session);
}
# update $product from other post/get data here, or from pulling data from another database here
# make sure to do $product->update({ }) with all data including the sku; the sku will match for existing products but it needs to be set if we just created this
$cart->addItem($product);