Extend category attribute set with select box (multiple choose) - php

Question

Im trying to accomplish a select box with multiple option-choose in the backend of categories.
The script to create a select box is working so far, but only with a single-choose.
$installer = $this;
$installer->startSetup();
$attribute = array(
'group' => 'Examplegroup',
'input' => 'select', // also tried multiselect
'type' => 'varchar',
'label' => 'Examplelabel',
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
'visible' => 1,
'required' => 0,
'visible_on_front' => 0,
'is_html_allowed_on_front' => 0,
'is_configurable' => 0,
'searchable' => 0,
'filterable' => 1,
'comparable' => 0,
'unique' => false,
'user_defined' => true,
'default' => '',
'is_user_defined' => false,
'used_in_product_listing' => true,
'option' => array('values' => array('option1', 'option2', 'option3', 'option4'))
);
$installer->addAttribute('catalog_category', 'attribute_name', $attribute);
$installer->endSetup();
How do I achieve this
I assume it should work with the input-type of multiselect but it keeps a single-choose-option after upgrading.

Answer 1

For multiselect option, set input to multiselect and add backend model eav/entity_attribute_backend_array.
$installer = $this;
$installer->startSetup();
$attribute = array(
'group' => 'Examplegroup',
'input' => 'multiselect',
'type' => 'varchar',
'label' => 'Examplelabel',
'backend' => 'eav/entity_attribute_backend_array',
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
'visible' => 1,
'required' => 0,
'visible_on_front' => 0,
'is_html_allowed_on_front' => 0,
'is_configurable' => 0,
'searchable' => 0,
'filterable' => 1,
'comparable' => 0,
'unique' => false,
'user_defined' => true,
'default' => '',
'is_user_defined' => false,
'used_in_product_listing' => true,
'option' => array('values' => array('option1', 'option2', 'option3', 'option4'))
);
$installer->addAttribute('catalog_category', 'attribute_name', $attribute);
$installer->endSetup();
Run the following upgrade script to update existing attribute,
$installer->startSetup();
$installer->updateAttribute('catalog_category', 'attribute_name', 'frontend_input', 'multiselect');
$installer->updateAttribute('catalog_category', 'attribute_name', 'backend_model', 'eav/entity_attribute_backend_array');
$installer->endSetup();
Check beforeSave function of Mage_Eav_Model_Entity_Attribute_Backend_Array class to get more idea of backend model.
Hope it helps!