add custom order attribute to the order from in magento admin

I've added a custom order attribute and updated the onepage checkout page. Now I'm trying to add this attribute to the new order form in the admin. I'm trying to extend Mage_Adminhtml_Block_Sales_Order_Create_Form_Account and add a new field in the _prepareForm() method similar to the way the Group and Email fields are added.

How do I get the order attribute? I've tried several ways but nothing works. This is how I'm creating the custom order attribute in the mysql-install file:

$attribute  = array(
        'type'          => 'int',
        'label'         => 'myattr',
        'visible'       => false,
        'required'      => false,
        'user_defined'  => false,
        'searchable'    => false,
        'filterable'    => false,
        'comparable'    => false,
);
$installer->addAttribute('order', 'myattr', $attribute);

and this is how I'm trying to get the attribute:

$res = Mage::getSingleton('core/resource');
$eav = Mage::getModel('eav/config');
$attr = $eav->getAttribute('sales/order', 'myattr');

or with this:

$entityType = Mage::getModel('eav/config')->getEntityType('order');
$entityTypeId = $entityType->getEntityTypeId();

$attribute = Mage::getResourceModel('eav/entity_attribute_collection')
                ->setCodeFilter('myattr')
                ->setEntityTypeFilter($entityTypeId)
                ->getFirs开发者_StackOverflow中文版tItem();

or this:

$order = Mage::getResourceSingleton('sales/order');
$myAttr = $order->getAttribute('myattr');

None of them work.

Have you verified that the attribute is being added to eav_attribute table in the database with the correct entity_type_id? (I think sales_order is 11 by default, but don't assume that)

At first glance, it looks like you should be using

$installer->addAttribute('sales/order', 'myattr', $attribute);

HTH, JD

Sales/Order used to use the EAV Model which supports attributes, that was before 1.4.0 or so not sure. I think now you should do:

$installer->getConnection()->addColumn($installer->getTable('sales/order'), 'my_column', 'decimal(12,4)');

you can still add the attribute as static field

$installer->addAttribute('order', 'my_column', array('type'=>'static'));

What I noticed after much trial-and-error was that the new attribute must have a default (non-null) value in order to work. Somehow the attribute is not writable if it has a 'NULL' value in the database. So using this attribute options array worked for me:

$attribute  = array(
'type'          => 'int',
'label'         => 'myattr',
'default'       => 0,
'visible'       => false,
'required'      => false,
'user_defined'  => true,
'searchable'    => false,
'filterable'    => false,
'comparable'    => false );