Magento: how to filter the result of Mage::getResourceModel('eav/entity_attribute_collection') by Category

I've used the follow code to get the whole list of manufacturer.

    $currentCategory = Mage::registry('current_category');
    $product = Mage::getModel('catalog/product');       
    $attributes = Mage::getResourceModel('eav/entity_attribute_collection')->setEntityTypeFilter($product->getRe开发者_如何学JAVAsource()->getTypeId())->addFieldToFilter('attribute_code', 'brand_name');      
    $attribute = $attributes->getFirstItem()->setEntity($product->getResource());       
    $manufacturers = $attribute->getSource()->getAllOptions(false);      

Now, how can I get the manufacturer list that belong to a specific category? I've been digging for a while to find out a way to limit the result by a category but no luck. Can ResourceModel filtered by Category?

Thanks.

---

I think you'd be better off starting with a collection of products from the category and then getting the attributes that match those products. Something like:

$currentCategory = Mage::registry('current_category');
$products = $currentCategory->getProductCollection();
foreach($products as $product):
  $product = Mage::getModel('catalog/product')->load($product->getId());
  $manufacturers[] = $product->getBrandName();      
endforeach;

You would need to deduplicate the array, but array_unique() should help you out there.

HTH, JD

EDIT

This will prevent the need to load each product, should improve performance:

$currentCategory = Mage::registry('current_category');
$products = $currentCategory->getProductCollection();
$products->addAttributeToSelect('brand_name');
$products->load();  //execute the query
$manufacturers = $products->toArray(array('brand_name'));

Keep in mind that with caching, the performance hit only costs you once.

JD

---

Thanks for the nice way to get the option id for the attribute. It really helped me a lot! Here is what I ended up doing to get the option id and its text value:

$currentCategory = Mage::registry('current_category');
$products = $currentCategory->getProductCollection();
$products->addAttributeToSelect('brand_name');
$products->load();  //execute the query
$manufacturers = $products->toArray(array('brand_name'));   
$temp = array();
foreach($manufacturers as $v) {
    $temp[] = $v['brand_name'];
}
$brands = implode(",",array_unique($temp));
$write = Mage::getSingleton('core/resource')->getConnection('core_write');
$readresult=$write->query("SELECT eav_attribute_option_value.option_id, eav_attribute_option_value.value FROM eav_attribute_option_value INNER JOIN eav_attribute_option ON eav_attribute_option_value.option_id=eav_attribute_option.option_id WHERE eav_attribute_option.attribute_id=505 AND eav_attribute_option_value.option_id IN (".$brands.")");

while ($row = $readresult->fetch() ) {
    $brandlist[] = array('value'=>$row['option_id'], 'label'=>$row['value']);
}

The brandlist array will have the option id and value so that I can use it to link.

Thanks again.