Limit product backorder qty

Question

Is there a way to limit the backorder qty? ie: I want to allow a product to get back-ordered, but only by a few

Answer 1

Not that I know.

hacky way

The easy way is to raise all your qty by X where X is the number of backorders you want to allow.

better way

But you could deactivate the observer which checks it:

\Mage_CatalogInventory_Model_Observer::checkQuoteItemQty()

and implement your own with your qty. The problem is, the actual check is made here:

\Mage_CatalogInventory_Model_Stock_Item::checkQty()

so the alternative is, to rewrite the catalog_inventory/stock_item model.

Answer 2

Further to Fabian's answer, you can see in Mage_CatalogInventory_Model_Stock_Item::checkQty there is the following:

public function checkQty($qty)
{
    if (!$this->getManageStock() || Mage::app()->getStore()->isAdmin()) {
        return true;
    }

    if ($this->getQty() - $this->getMinQty() - $qty < 0) {
        switch ($this->getBackorders()) {
            case Mage_CatalogInventory_Model_Stock::BACKORDERS_YES_NONOTIFY:
            case Mage_CatalogInventory_Model_Stock::BACKORDERS_YES_NOTIFY:
                break;
            default:
                return false;
                break;
        }
    }
    return true;
}

This basically gives backorders a free pass on the quantity check.

To have the non-backorder checks (e.g. 'Some of the products are currently out of stock' and 'The requested quantity for product is not available') apply you need three things:

1. a way to set the allowed backorder quantity per product.
2. use this attribute in checkQty (or similar).
3. have checkQty return false if cart quantity + quantity sold exceeds allowed quantity.

More details here: https://magento.stackexchange.com/a/41361/788

An extension I wrote to do this is here: https://github.com/etailer/etailer_backorders