Understand product attribute type multiselect

Question

Do you know why magento saves multiselect attribute type as varchar and relative product assocations in catalog_product_entity_varchar as array?

With array is not possible join between catalog_product_entity_varchar and eav_attribute_option_value on value=option_id

when value is varchar like 1,2,3, because option_id is int.

Isn't better considerer multiselect as multiple int and insert multiple record in catalog_product_entity_int?

So is possible join correctly catalog_product_entity_int and eav_attribute_option_value on value=option_id

Answer 1

Multiselect attributes can be set as a comma separated list (or also an array) containing the attribute value ids.

So first we have to convert the actual values to Magento's internal ids. try this code:-

$attrCode = 'color_base';
$sourceModel = Mage::getModel('catalog/product')->getResource()
    ->getAttribute($attrCode)->getSource();
$valuesText = explode(',', 'red,green,blue');
$valuesIds = array_map(array($sourceModel, 'getOptionId'), $valuesText);
$product->setData($attrCode, $valuesIds);
$product->save();

link:-http://swarminglabs.com/how-to-change-a-product-dropdown-attribute-to-a-multi-select/