Magento: Setting custom shipping method programmatically - php

Question

I'm pretty new to Magento, and having problems trying to set a custom shipping method programmatically. I'm converting an xml from a thrid party into an order, and everything else (that I've worked on so far) is working fine. Also I'm having problems spelling "programmatically" but I won't ask for you help with that.
I set up my custom shipping method as follows:
To activate the shipping module in
app/etc/modules/Extension_Shipping.xml
<?xml version=
"1.0"?>
<config>
<modules>
<Extension_Shipping>
<active>true</active>
<codePool>local</codePool>
<depends>
<Mage_Shipping/>
</depends>
</Extension_Shipping>
</modules>
</config>
then to configure it in
app/code/local/Extension/Shipping/etc/config.xml
<?xml version=
"1.0" ?>
<config>
<modules>
<Extension_Shipping>
<version>0.1.0</version>
</Extension_Shipping>
</modules>
<global>
<models>
<extension_shipping>
<class>Extension_Shipping_Model</class>
</extension_shipping>
</models>
</global>
<default>
<carriers>
<extension_myrate>
<active>1</active>
<model>extension_shipping/carrier_myrate</model>
<title>Extension Shipping</title>
<name>Default Rate</name>
</extension_myrate>
</carriers>
</default>
</config>
then to add the class in
app/code/local/Extension/Shipping/Model/Carrier/MyRate.php
<?php
class Extension_Shipping_Model_Carrier_MyRate
extends Mage_Shipping_Model_Carrier_Abstract
implements Mage_Shipping_Model_Carrier_Interface
{
protected $_code = 'extension_myrate';
protected $_isFixed = true;
public function collectRates(Mage_Shipping_Model_Rate_Request
$request)
{
if (!$this->getConfigFlag('active')) {
return false;
}
$result = Mage::getModel('shipping/rate_result');
$method = Mage::getModel('shipping/rate_result_method');
$method->setCarrier('extension_myrate');
$method->setCarrierTitle($this->getConfigData('title'));
$method->setMethod('extension_myrate');
$method->setMethodTitle($this->getConfigData('name'));
$method->setPrice(5);
$method->setCost(2);
$result->append($method);
return $result;
}
public function getAllowedMethods()
{
return array('extension_myrate' => $this->getConfigData('name'));
}
}
Basically I followed http://www.magentotricks.com/creating-a-customer-magento-shipping-method/
I thought it all worked fine, as the shipping method now shows up in the checkout screen, and can be set both by customers or in the admin "create new order." However, I'm not able to set it programmatically.
In my controller I'm trying to set the shipping method using the code
$shippingAddress = $quote->getShippingAddress()->addData($addressData);
$shippingAddress->setCollectShippingRates(true)->collectShippingRates()
->setShippingMethod('extension_myrate')
->setPaymentMethod('checkmo');
To add to my confusion, it worked once. but only once out of quite a few test orders. changing the "setShippingMethod" to "freeshipping_freeshipping" or "flatrate_flatrate" makes it update the shipping to those correctly. because of that and because I'm new and still having problems with the file structure, I'm guessing my problem is with setShippingMethod('extension_myrate') but I'm not entirely sure. Any advice would be helpful and appreciated.