如何在Magento Api的产品列表方法结果中包含产品图像

Question

I want to minimize the number of Api calls for a mobile application which connects to Magento based shop to display products. right now we have to call catalog_product_attribute_media.list method for each product in order to get image Urls and it really slows down the app.

I found out in this answer that it is possible to extend the result of an Api Call by editing certain scripts. I tried to use the same approach to include images in product list by editing app/code/core/Mage/Catalog/Model/Category/Api.php line 440:

$storeId = $this->_getStoreId($store);
$collection = $category->setStoreId($storeId)->getProductCollection()
->addAttributeToSelect('brand')
->addAttributeToSelect('media_gallery_images');
($storeId == 0)? $collection->addOrder('position', 'asc') : $collection->setOrder('position', 'asc');;

$result = array();

foreach ($collection as $product) {
    $result[] = array(
        'product_id' => $product->getId(),
        'type'       => $product->getTypeId(),
        'set'        => $product->getAttributeSetId(),
        'sku'        => $product->getSku(),
        'position'   => $product->getCatIndexPosition(),
        'brand'      => $product->getData('brand'),
    'media'      => $product->getMediaGalleryImages()
    );
}

return $result;

I also edited html/app/code/core/Mage/Catalog/etc/wsdl.xml to include the new 'media' property line: 255

    <complexType name="catalogAssignedProduct">
        <all>
            <element name="product_id" type="xsd:int"/>
            <element name="type" type="xsd:string"/>
            <element name="set" type="xsd:int"/>
            <element name="sku" type="xsd:string"/>
            <element name="position" type="xsd:int"/>
            <element name="brand" type="xsd:string"/>
            <element name="media" type="typens:catalogProductImageEntityArray"/>
        </all>
    </complexType>

but when I call the catalog_category.assignedProducts it always returns null for the 'media' property, I wonder why this doesn't work? is it the xml type or something else?