Magento - addCategoryFilter throws an error

I'm successfully running this query:

 $_productCollection = Mage::getResourceModel('reports/product_collection')
                        ->addAttributeToSelect('*')
                        ->set开发者_运维问答Order('created_at', 'desc')
                        ->setPage(1, 5);

but when I add

->addCategoryFilter('3')

I got the following error:

Fatal error: Call to a member function getId() on a non-object in /home/sitename/public_html/app/code/core/Mage/Catalog/Model/Resource/Eav/Mysql4/Product/Collection.php on line 556

The block it is running at is defined as

<block type="catalog/product_list" name="catalog.right.bestsellers" template="catalog/navigation/right.phtml"/>

at catalog.xml

---

This covers 1.4.2. Based on your error, I think you're running a slightly older version, but the root cause of your error should be the same.

The class alias reports/product_collection resolves to

Mage_Reports_Model_Mysql4_Product_Collection

in resource mode context. The class Mage_Reports_Model_Mysql4_Product_Collection is a child of Mage_Catalog_Model_Resource_Eav_Mysql4_Collection_Abstract. The addCategoryFilter on Mage_Catalog_Model_Resource_Eav_Mysql4_Collection_Abstract looks like this

public function addCategoryFilter(Mage_Catalog_Model_Category $category)
{
    $this->_productLimitationFilters['category_id'] = $category->getId();
    if ($category->getIsAnchor()) {
        unset($this->_productLimitationFilters['category_is_anchor']);
    }
    else {
        $this->_productLimitationFilters['category_is_anchor'] = 1;
    }

    ($this->getStoreId() == 0)? $this->_applyZeroStoreProductLimitations() : $this->_applyProductLimitations();

    return $this;
}

Notice that in 1.4.2 there's some type checking going on in the paramaters

public function addCategoryFilter(Mage_Catalog_Model_Category $category)

I suspect your version doesn't have that checking. Therefore, it fails when it reaches

$this->_productLimitationFilters['category_id'] = $category->getId();

You're passing in a string, and then Magento tries to call getId on the string. That's why you get an error.

Magento expects you to pass in a category object, and not a category ID. Give this a try

$category = Mage::getModel('catalog/category')->load(3);
$p = Mage::getResourceModel('reports/product_collection')
            ->addAttributeToSelect('*')
            ->setOrder('created_at', 'desc')
            ->addCategoryFilter($category)
            ->setPage(1, 5);

---

The parameter for addCategoryFilter() must be an object of type Mage_Catalog_Model_Category.