Magento - Override/extend Ebizmarts_SagePaySuite_Model_Api_Payment model class - magento

Question

I am trying to override/extend the Ebizmarts SagePay Suite Ebizmarts_SagePaySuite_Model_Api_Payment model class
My module looks like this:
etc/modules/Sulman_ModifySagePay.xml
<?xml version="1.0"?>
<config>
<modules>
<Sulman_ModifySagePay>
<active>true</active>
<codePool>local</codePool>
<version>1.0</version>
<depends>
<Ebizmarts_SagePaySuite />
</depends>
</Sulman_ModifySagePay>
</modules>
</config>
app/code/local/Sulman/ModifySagePay/etc/config.xml
<?xml version="1.0"?>
<config>
<modules>
<Sulman_ModifySagePay>
<version>0.0.1</version>
</Sulman_ModifySagePay>
</modules>
<global>
<models>
<sagepaysuite>
<rewrite>
<api_payment>Sulman_ModifySagePay_Model_Api_Payment</api_payment>
</rewrite>
</sagepaysuite>
</models>
</global>
</config>
app/code/local/Sulman/ModifySagePay/Model/Api/Payment.php
<?php
class Sulman_ModifySagePay_Model_Api_Payment extends Ebizmarts_SagePaySuite_Model_Api_Payment {
public function _construct(){
Mage::log('in my construct()', null, 'Sulman.log');
}
public function requestPost($url, $data, $returnRaw = false) {
Mage::log('in my requestPost()', null, 'Sulman.log');
}
}
Nothing gets logged and this gives me errors on the checkout page because:
When I check to see if it is instantiated it returns false (if I disable my module it returns the Ebizmarts_SagePaySuite_Model_Api_Payment object):
var_dump(Mage::getModel('sagepaysuite/api_payment'));
Other calls to this model throughout the site also fail.
I'm a little confused as it seems my rewrite is working correctly but it can't seem to find my new model class.
Anyone have any ideas where I'm going wrong?
Thanks

Answer 1

In your app/code/local/Sulman/ModifySagePay/etc/config.xml in the <models></models> section you need to define where your models are located:
<models>
<modifysagepay>
<class>Sulman_ModifySagePay_Model</class>
<modifysagepay>
</models>