Setting the strategy in a Strategy Pattern - php

Question

I might have implementing this wrong as I cannot figure out a solid way of setting which strategy to use in my implementation of the Strategy Pattern. I'm not a big fan of writing it "statically", perhaps there is another way.
Backstory: I've done two (2) implementations (soap + http) to shipping providers in order to retrieve Track & Trace information for whatever the user inputs frontend. They each follow an interface so that I know which functions are and should (PHP :3) be available. I've shortened the class names below as this is Magento and class names are very long.
Flow: Customer inputs tracking number in a form and submits. Request is sent to the controller, controller initializes an instance of Service class, sets output via. $service->setOutput('tracking/service_gls') - note that tracking/service_gls just maps directly to the service class (Magento thing), $service->getDeliveryInformation($number) is called (we know this exists because of the interface), the entire $service object is returned to the view and data is presented.
My challenge: I'm using a switch case to set tracking/service_gls and tracking/service_otherservice then calling getDeliveryInformation(). Is this the correct approach? I feel it's a bit too static and hard to maintain if someone wants to connect another shipping provider. They would have to enter the controller and manually add another entry to the switch case, in a function somewhere 200 lines deep in the class.
Example of how the controller looks:
public function getDeliveryInformationAction()
{
$id = $this->getRequest()->getParam('id', false);
if ($id && $this->getRequest()->isAjax())
{
// SO note: service parameter is just two radio buttons with values "gls", "otherservice"
$serviceType = $this->getRequest()->getParam('service', false);
try
{
// SO note: same as doing new Class()
$service = Mage::getModel('tracking/service');
switch ($serviceType)
{
case 'gls':
$service->setOutput('tracking/service_gls');
break;
case 'other':
$service->setOutput('tracking/service_other');
break;
}
$shipment = $service->getDeliveryInformation($id);
$output = // .. create block that contains the view, $output will contain the shipment data; this is returned to the ajax request.
}
catch (Exception_RequestError $e)
{
..
}
// finally
$this->getResponse()->setHeader('content-type', 'text/html', true);
$this->getResponse()->setBody($output);
}
}
Code has been shortened a bit as there are lots more functions, but not important.
Interface the two shipping provider models are implementing
interface Output
{
/* Requests delivery information for the specified tracking number */
public function getDeliveryInformation($number);
/**
* Returns acceptor name
* #return string
*/
public function getAcceptorName();
}
Service class handles requesting data from the shipping models
class Service
{
protected $output;
/**
* Sets the output model to use
* #param string $outputType
*/
public function setOutput($outputModel)
{
// SO note: same as doing new Class()
// Magento people note: getModel() works fine tho.. ;-)
$modelInstance = Mage::app()->getConfig()->getModelInstance($outputModel);
$this->output = $modelInstance;
}
/**
* Returns delivery information for the specified tracking number
* #param string $number
* #return instance of output class
*/
public function getDeliveryInformation($number)
{
// SO note: This makes the shipping class request
// information and set data internally on the object
$this->output->getDeliveryInformation($number);
return $this->output;
}
}
Example of a shipping class; I have two in this case
class Service_Gls implements Output
{
const SERVICE_NAME = 'GLS';
const SERVICE_URL = 'http://www.gls-group.eu/276-I-PORTAL-WEBSERVICE/services/Tracking/wsdl/Tracking.wsdl';
protected $locale = 'da_DK';
/* Class constructor */
public function __construct() { }
/**
* Requests delivery information for the specified tracking number
* #param mixed $number
*/
public function getDeliveryInformation($number)
{
$this->_getDeliveryInformation($number);
}
/**
* Requests and sets information for the specified tracking number
* #param mixed $number
*/
private function _getDeliveryInformation($number)
{
// SO note: Extending from Varien_Object has magic __get, __set .. hence why there is no getData() function in this class.
if (!count($this->getData()))
{
$client = new SoapClient($url);
$client->GetTuDetail($reference));
.. set data
}
}
/**
* Returns acceptor name
* #return string
*/
public function getAcceptorName()
{
$signature = $this->getSignature();
return (isset($signature)) ? $this->getSignature() : false;
}
/**
* Returns the name of the current service
* #return string
*/
public function __toString()
{
return self::SERVICE_NAME;
}
}
Controller
class AjaxController extends Mage_Core_Controller_Front_Action
{
public function getDeliveryInformationAction()
{
$id = $this->getRequest()->getParam('id', false);
if ($id && $this->getRequest()->isAjax())
{
// SO note: service parameter is just two radio buttons with values "gls", "otherservice"
$serviceType = $this->getRequest()->getParam('service', false);
try
{
$service = Mage::getModel('tracking/service');
switch ($serviceType)
{
case 'gls':
$service->setOutput('tracking/service_gls');
break;
case 'other':
$service->setOutput('tracking/service_other');
break;
}
$shipment = $service->getDeliveryInformation($id);
$output = // .. create block that contains the view, $output will contain the shipment data; this is returned to the ajax request.
}
catch (Exception_RequestError $e)
{
..
}
// finally
$this->getResponse()->setHeader('content-type', 'text/html', true);
$this->getResponse()->setBody($output);
}
}
}

Answer 1

Well you either do it with a switch or with some sort of string concatenation to return the strategy class you need.
With the Strategy Pattern, choosing the correct strategy at run time is usually done through a StrategyContext pattern: https://sourcemaking.com/design_patterns/strategy/php . This allows you to isolate the algorithm to choose the correct strategy so it is not "in a function somewhere 200 lines deep in the class." .
As to the algorithm for setting the runtime strategy, personally I am a fan of class constants rather than string manipulation etc. Since the aim of the game is to arrive at a class name to instantiate, why not just a class constant to return the class name.
class OutputStrategyContext{
const SERVICE = 'tracking/service_gls';
const OTHER = 'tracking/service_other';
private $strategy;
public function __construct($serviceType)
{
$strategy = constant('self::' . strtoupper($serviceType));
$modelInstance = Mage::app()->getConfig()->getModelInstance($strategy);
$this->strategy = $modelInstance;
}
public function getStrategy()
{
return $this->strategy;
}
}
Lightweight and easy to maintain, the list of strategy classes is in one place.
You can of course make the whole thing static, or use another design pattern like an abstract factory method to acheive the same thing. Up to you really.
Anyway in the controller it is a one-liner
class AjaxController extends Mage_Core_Controller_Front_Action
{
public function getDeliveryInformationAction()
{
$id = $this->getRequest()->getParam('id', false);
if ($id && $this->getRequest()->isAjax())
{
// SO note: service parameter is just two radio buttons with values "gls", "otherservice"
$serviceType = $this->getRequest()->getParam('service', false);
try
{
$service = Mage::getModel('tracking/service');
$outputModel = new OutputStrategyContext($serviceType)->getStrategy();
$service->setOutput($outputModel);
$shipment = $service->getDeliveryInformation($id);
$output = // .. create block that contains the view, $output will contain the shipment data; this is returned to the ajax request.
}
catch (Exception_RequestError $e)
{
..
}
// finally
$this->getResponse()->setHeader('content-type', 'text/html', true);
$this->getResponse()->setBody($output);
}
}
}
Of course you have to modify the service . I also modified my context class for your code.
class Service
{
protected $output;
/**
* Sets the output model to use
* #param string $outputType
*/
public function setOutput($outputModel)
{
// SO note: same as doing new Class()
// Magento people note: getModel() works fine tho.. ;-)
$this->output = $outputModel;
}
/**
* Returns delivery information for the specified tracking number
* #param string $number
* #return instance of output class
*/
public function getDeliveryInformation($number)
{
// SO note: This makes the shipping class request
// information and set data internally on the object
$this->output->getDeliveryInformation($number);
return $this->output;
}
}