Magento - How to create "decimal" attribute type - magento

Question

I've done a bit of searching online but I have not found any answers to this question yet. I have a situation where I need a product attribute that is a decimal value and it must support negative numbers as well as positive and must also be sortable. For some reason, Magento does not have a "decimal" attribute type. The only type that uses decimal values is Price, but that doesn't support negative numbers. If I use "text" as the type, it supports whatever I want, but it doesn't sort properly because it sees the values as strings rather than floating point numbers. I have been able to work around this issue, as others have in posts I've found, by manually editing the eav_attribute table and changing 'frontend_input' from 'price' to 'text', but leaving the 'backend_type' as 'decimal'. This works great...until someone edits the attribute in the admin panel. Once you save the attribute, Magento notices that the frontend_input is 'text' and changes the 'backend_type' to 'varchar'. The only way around this that I can think of is by creating a custom attribute type, but I'm not sure where to start and I can't find any details online for this.
Has anyone else experienced this problem? If so, what have you done to correct it? If I need to create a custom attribute type, do you have any tips or can you point me at any tutorials out there for doing this?
Thanks!

Answer 1

What you want to do is create a custom attribute type.
This can be done by first creating a installer script (this updates the database).
startSetup();
$installer->addAttribute('catalog_product', 'product_type', array(
'group' => 'Product Options',
'label' => 'Product Type',
'note' => '',
'type' => 'dec', //backend_type
'input' => 'select', //frontend_input
'frontend_class' => '',
'source' => 'sourcetype/attribute_source_type',
'backend' => '',
'frontend' => '',
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_WEBSITE,
'required' => true,
'visible_on_front' => false,
'apply_to' => 'simple',
'is_configurable' => false,
'used_in_product_listing' => false,
'sort_order' => 5,
));
$installer->endSetup();
After that you need to create a custom php class named:
Whatever_Sourcetype_Model_Attribute_Source_Type
And in there paste this in:
class Whatever_Sourcetype_Model_Attribute_Source_Type extends Mage_Eav_Model_Entity_Attribute_Source_Abstract
{
const MAIN = 1;
const OTHER = 2;
public function getAllOptions()
{
if (is_null($this->_options)) {
$this->_options = array(
array(
'label' => Mage::helper('sourcetype')->__('Main Product'),
'value' => self::MAIN
),
array(
'label' => Mage::helper('sourcetype')->__('Other Product'),
'value' => self::OTHER
),
);
}
return $this->_options;
}
public function toOptionArray()
{
return $this->getAllOptions();
}
public function addValueSortToCollection($collection, $dir = 'asc')
{
$adminStore = Mage_Core_Model_App::ADMIN_STORE_ID;
$valueTable1 = $this->getAttribute()->getAttributeCode() . '_t1';
$valueTable2 = $this->getAttribute()->getAttributeCode() . '_t2';
$collection->getSelect()->joinLeft(
array($valueTable1 => $this->getAttribute()->getBackend()->getTable()),
"`e`.`entity_id`=`{$valueTable1}`.`entity_id`"
. " AND `{$valueTable1}`.`attribute_id`='{$this->getAttribute()->getId()}'"
. " AND `{$valueTable1}`.`store_id`='{$adminStore}'",
array()
);
if ($collection->getStoreId() != $adminStore) {
$collection->getSelect()->joinLeft(
array($valueTable2 => $this->getAttribute()->getBackend()->getTable()),
"`e`.`entity_id`=`{$valueTable2}`.`entity_id`"
. " AND `{$valueTable2}`.`attribute_id`='{$this->getAttribute()->getId()}'"
. " AND `{$valueTable2}`.`store_id`='{$collection->getStoreId()}'",
array()
);
$valueExpr = new Zend_Db_Expr("IF(`{$valueTable2}`.`value_id`>0, `{$valueTable2}`.`value`, `{$valueTable1}`.`value`)");
} else {
$valueExpr = new Zend_Db_Expr("`{$valueTable1}`.`value`");
}
$collection->getSelect()
->order($valueExpr, $dir);
return $this;
}
public function getFlatColums()
{
$columns = array(
$this->getAttribute()->getAttributeCode() => array(
'type' => 'int',
'unsigned' => false,
'is_null' => true,
'default' => null,
'extra' => null
)
);
return $columns;
}
public function getFlatUpdateSelect($store)
{
return Mage::getResourceModel('eav/entity_attribute')
->getFlatUpdateSelect($this->getAttribute(), $store);
}
}
Hope this helps.
For further info see here.