Delegate Rendering in Symfony

Warning: pretty advanced Symfony ahead: if you’re not familiar with the framework, this wouldn’t make sense.

I recently developed a bare-bones API for Mobshare (it’s not yet live), and to keep everything clean, I abstracted away the rendering bit from the controller to an external class. It ended up being a sweet solution, so here it is!

I wanted this to be a JSONP API (the major use case would be a JS client, and parsing XML etc. via JS is a pain. Besides JSON is much shorter over the wire). I didn’t want to rewrite a lot of code: checking for a callback parameter and wrapping the returned string around the JSON output was just begging to be refactored away. So here it is, a generic Symfony JSON API wrapper class:


<?php

class JSONPAPI {

	const CALLBACK_PARAMETER = 'callback';

	var $status;
	var $data;
	var $callback;


	public function __construct($status, $data) {
		$this->status = $status;
		$this->data = $data;

		$callback_parameter_value = $this->getCurrentAction()->getRequestParameter(self::CALLBACK_PARAMETER);
		if($callback_parameter_value)
			$this->callback = $callback_parameter_value;
	}

	public function render() {
		$render_text = json_encode(array($this->status => $this->data));

		if($this->callback)
			$render_text = $this->callback . '(' . $render_text . ');';

		$this->setJavascriptHeaders();
		return $this->getCurrentAction()->renderText($render_text);
	}

	//hack to get the current action
	private function getCurrentAction() {
		return sfContext::getInstance()->getActionStack()->getLastEntry()->getActionInstance();
	}

	private function setJavascriptHeaders() {
		sfContext::getInstance()->getResponse()->setParameter('Content-Type', 'application/javascript', 'symfony/response/http/headers');
	}
}

The bits of magic here are the getCurrentAction() function and the render() call. It works on one very simple idea: everything in Symfony can be accessed from the sfContext::getInstance() object, you just need to dig deep enough.

Once you write this boiler-plate code, using it is very elegant. First, subclass it for your API:


<?php

require_once('JSONPAPI.class.php');

class MobshareAPI extends JSONPAPI {


}

And then, use it like so within your controller:


<?php
class userActions extends sfActions
{

	public function executeAuthenticate() {
		$valid_user = UserPeer::authenticate($this->getRequestParameter('alias'),
			$this->getRequestParameter('mobile_no'), $this->getRequestParameter('password'));
		if($valid_user instanceOf User) {
			$success = new MobshareAPI('success', $valid_user->toArray());
			return $success->render();
		} else {
			$error = new MobshareAPI('error', 'Authentication failed: Alias, mobile number or password invalid.');
			return $error->render();
		}
	}

}

Note: the rendering has been delegated to the $success and $error MobshareAPI objects. This allows for a really maintainable API. Adding functionality is much simpler since you don’t have to worry about the boilerplate.

You end up calling the API like this:


http://api.mobshare/user/authenticate?alias=vish&password=xxx&callback=handler

and you get back data which looks like this:


handler({"success":{"alias":"vish","name":"Vishnu Gopal","photo_mini": ...);

Note that callback handling is done entirely by the API and the controller needn’t worry about this parameter at all!

Published by vishnugopal

Vishnu Gopal is an Anime fanatic, World of Warcraft player, SciFi nut, hopeless romantic & CTO at SV.CO.

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  1. it looks really nice, thanks for the tip… i was wondering how to render json with symfony in a clean manner.

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