Filter product collection by multiple categories in Magento

During the past week I’ve dealed with a very weird and stressing thing with my colleagues: filtering a product collection by multiple categories in Magento.

  • Filter by only 1 category

Magento offers a type of filter that can be used directly from the collection:

$_category = Mage::getModel('catalog/category')->load($category_id);

  • Filter by 2 or more categories

This is a completely different story. It’s very important to proceed correctly in order to avoid errors of the type:
[blockquote]Item (Mage_Catalog_Model_Product) with the same id already exist[/blockquote]

Proceed in the following way:

1. Call your collection and filter by the attributes you want to filter (all but the category one). For example:

$collection= Mage::getResourceModel('catalog/product_collection')
           ->addFieldToFilter('type_id', array('eq' => 'configurable'));

2. After doing this, you can apply your multiple category filter as follows:

$categories_to_filter = array('3', '4', '5');
$ctf = array();

foreach ($categories_to_filter as $k => $cat) {
     $ctf[]['finset'] = $cat;

$collection->joinField('category_id', 'catalog/category_product', 'category_id', 'product_id = entity_id', null, 'left')

Important: do it in this order if you don’t want to face weird Magento issues.

    • Greg on May 25, 2013 at 8:02 am


    This filters multiple categories using an OR condition – is there any way to do this with an AND condition to get products which are in both category X and category Y?

  1. Reply


    I nub in magento developpement, and when I read your post I have just one question :
    Where (in which file) do you put your code? ( In nmy case, I want this filter on left side in “Shop By” or “Browse By” block) ?

    Thanks for your answer

      • Pau on September 29, 2013 at 7:04 am
      • Author


      Hi Julien,

      I created a php script with this code that I put on my shell folder. After that, I executed the script using the terminal: php script.php.

      You will need to find some information on how to create Magento Shell Scripts.

  2. Reply

    Thanks for sharing this. I too struggled with this a few weeks ago. Kinda a thorn in my side trying to figure it out 🙂

    • Nasir Perwaiz on August 18, 2014 at 11:00 am



    Using the above code gives me the following error,

    Joined field with this alias is already declared

    Any idea how to solve it.


    Nasir Perwaiz

  3. Reply

    Thanks a lot! Its really helpfull. I have tried to lot to do the same but nothing was working and finally it helped me. 🙂

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