Magento – How to create an Add to Cart button to add multiple products

Ok description is not loaded by default so what I had do was ugly way of displaying description on related product.

In foreach loop you can get product id from this $_item->getEntityId()

And from id load product model $product = Mage::getModel('catalog/product')->load($_item->getEntityId());

$product->getDescription() give you description of product.

And for add to cart button remove your checkbox input field put something like this

<a href="<?php echo Mage::getBaseUrl() ?>checkout/cart/add/product/<?php echo $_item->getId();?>">Add to cart </a>

thus you can have individual add to cart link.

You may want to take a look at getBuyRequest in app/code/core/Mage/Sales/Model/Quote/Item.php.

This method appears to be used to pull the product options, and then add them to the quote.

However, you would also want to modify the setProduct method as well, so that way you can setQty() on the Product being saved to the model to reference later in buyRequest.

You could do something like:

->setQty(Mage::getModel('cataloginventory/stock_item')->loadByProduct($product)->getQty())

in setProduct().

I wouldn't recommend doing these things in app/code/local/Mage overrides though, it would definitely be better to create a module for these things. In fact, you could accomplish this through an Observer event, listening for sales_quote_item_save_before and do something similar to:

public function checkQuoteItemQty($obs) {
    $event = $obs->getEvent();
    $item = $event->getDataObject();

    $product = Mage::getModel('catalog/product')->load($item->getProduct()->getProductId());
    $itemInventory = Mage::getModel('cataloginventory/stock_item')->loadByProduct($product);

    if ($item->getQty() > $itemInventory->getQty()) {
        $item->setQty($itemInventory->getQty());
    }

    return $this;
}

Hope this helps!