getting error after change attribute input type

Question

I have a page that I getting all products with some attributes. (room, color, size, price)

I change "Catalog Input Type for Store Owner" for room attribute on database. It was dropdown, now multiselect.

After this change the page returning null. Is anyone know why?

It's the part of code:

$room = $_POST['room'];
$collection = Mage::getResourceModel('reports/product_collection')
    ->addAttributeToSelect('*')
    //->addAttributeToFilter('color', 7)
    ->joinField('category_id', 'catalog/category_product', 'category_id', 'product_id=entity_id', null, 'left')
    ->addAttributeToFilter('category_id', array('in' => $catID))
    ->addAttributeToFilter('size', array('in'=>$size))
    ->addAttributeToFilter('room', array('in'=>$room))
    ->addStoreFilter()
    ->setOrder('created_at', 'desc')
    ->setPage($pageNumber, $productPerPage)
    ->setVisibility(Mage::getSingleton('catalog/product_visibility')->getVisibleInCatalogIds());
    //$collection->getSelect()->order('rand()');
    //$collection->getSelect()->limit(12);
    $collection->addAttributeToFilter('price', array('gt'=>$priceL));
    $collection->addAttributeToFilter('price', array('lt'=>$priceG));

Edit: If I remove "->addAttributeToFilter('room', array('in'=>$room))" line, it's perfectly working.

Answer 1

I assume that $room is one of the values from the available options of the room attribute.
Since the multiselects are saved in the db as a string with values concatenated by comma (1,4,5,6,7,15), you need to filter like this:

->addAttributeToFilter('room', array('finset'=>$room));

If the $room variable is an array you need to apply a multiple FIND_IN_SET filter with or condition.
See an example for this kind of filter in here