Magento – Admin to see Quantity change history of a product

This sounds like a similar issue I had about a year ago.

The end result was the same as what you have: totals got doubled by qty (qty * qty)

The problem was tracked down to when customer address got added to the order object, it got added twice as delivery address. Thus the order object had 3 addresses:

• 1 - Billing
• 2 - Shipping
• 3 - shipping (duplicate of #2)

I forget why this happened :( (I seem to recall an observer event doing something funky)

The same happened to the quote object (thus cart)

Since totals calculation hang directly off address objects, totals got doubled by qty.

An easy why to test if you are having the same issue, wipe out the sales_flat_order_address table, and enter checkout. Then check the table for address entries for your order. you should have 2 entries in there.

Additionally, since the issue is related to database entries, once the bug was fixed, it looked like the problem remained/was not fixed. It required removing the duplicates from the database for the problem to resolve for existing quote/order objects.

First thing's first:

• At present your current code is re-querying the database for the inventory information on every iteration of the loop. Don't call Mage::getModel in a loop... ever
• With that in mind, you probably don't want to ask Magento to get a model inside the template file either. So you probably want to add some method to your block to get the maximum quantity available in the database and then stop creating <option>s when you reach that limit.

Assuming the above is true you should create a custom module with a custom block. The template file you're currently editing should be modified to read as such:

<?php echo $this->getChildHtml('quantityoptionsdropdown');?>

Then in your layout xml (possibly local.xml) you'll have to define that alias block:

<catalog_product_view>
    <block type="yourcompany/options" template="yourcompany/options.phtml" name="quantityoptionsdropdown" as="quantityoptionsdropdown"/>
</catalog_product_view>

Notice that we used yourcompany/options there - which should map to your custom module's block class named Options. So the full class path (at least for this example) would be something like YourCompany_YourModule_Block_Options.

So this is what your block class would look like:

app/code/local/YourCompany/YourModule/Block/Options.php

class YourCompany_YourModule_Block_Options extends Mage_Core_Block_Abstract
{
    public function getStockMaximumQty()
    {
        $product = $this->getProduct();

        return $this->getProduct()->getStockItem()->getQty();
    }

    public function getProduct()
    {
        if(!$this->product){
            $this->product = Mage::registry('current_product');
        }
        return $this->product;
    }
}

Now, your template file:

app/design/frontend/base/default/template/yourcompany/options.phtml

<?php if($this->getStockMaximumQty()>0): ?>
    <? $i = 0; ?>
    <select name="quantity" id="qty">
        <?php while($i<=$this->getStockMaximumQty():?>
        <option value="<?php echo $i; ?>"><?php echo $i++; ?></option>
        <?php endwhile; ?>
    </select>
<?php else: ?>
    <?php echo $this->__('This product is currently out of stock.'); ?>
<?php endif; ?>