Using **Magento 1.8v**.

In my customization when customer adding products to **cart**.
Some products qty should not be changeable **(i.e qty is fixed)** and some other products **qty available** to change .

Example :

```
cat1 
  products 
cat2
  subcat
    products
  subcat
    products
cat3
  subcat
     products

```

**For Example:**
 cat1 products allowed for qty change so when adding to shopping cart it will be 1 and remaining category should not allowed so it is stock item value .

Im trying below code in this class `Mage/Checkout/Model/Cart.php` but throwing error

```
$categoryIds=$this->getProduct()->getCategoryIds($productid);
    foreach($categoryIds as $categoryId)    
    $category = Mage::getModel('catalog/category')->load($categoryId);
    if ($category->getName() == 'cat1')   
        $minimumQty = $product->getStockItem()->getMinSaleQty();  
   else if($category->getName() == 'cat2')                        
         minimumQty=stock_item->loadByProduct($product)->getQty();   

```

How do i get category name ?