I followed this tutorial here: http://inchoo.net/ecommerce/magento/how-to-create-custom-attribute-source-type/
In this tutorial, there are two key settings which I want to change:
'type' => 'int', //backend_type 'input' => 'select', //frontend_input
I tried using this:
'type' => 'varchar', //backend_type 'input' => 'multiselect', //frontend_input
This works great from a UI standpoint, but I can't get Magento save any selection when I have the attribute setup this way.
How can I make a custom attribute source model that fully supports multiselect?