Tag Archives: Software engineering

Zend Framework: Cache Database Table Schemes

micro tutorial, PHP, zend framework, , , , , ,

If you’re familiar with Zend Framework, you should know how to turn your database tables into models. Simply extend the Zend_Db_Table class. This is the very general example. There are lots of variations how to name the model classes and what member variables they can have.

<?
class User extends Zend_Db_Table
{}

The question is …

The question is how the framework knows what columns there are in a given table. That’s done by PHP on every call of the class, and the question is: isn’t that too slow? Yes it is and there’s a solution – to cache the table’s schema:

Zend_Db_Table_Abstract::setDefaultMetadataCache($cache);

Is there any problem?

Why it isn’t a default behavior when it’s so good? Because you’ve first to setup the cache, which is not always permitted – at least you’ve to have writing permissions. And on the second place if you’re rapidly developing the system and you change the database schema too frequently, you’ve to clear the cache every time. So it’s a good solution for the production server, but you can skip it while developing.

Friday Algorithms: A Data Structure: JavaScript Stack

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Algorithms and Data Structures

stack

Instead of writing about “pure” algorithms this time I’ve decided to write about data structures and to start with a stack implementation in JavaScript. However algorithms and data structures live together since the very beginning of the computer sciences. Another reason to write about data structures is that many algorithms need a specific data structure to be implemented. Most of the search algorithms are data structure dependent. You know that searching into a tree is different from searching into a linked list.

I’d like to write more about searching in my future algorithm posts, but first we need some data structure examples. The first one is, as I mentioned – stack.

Implemented in JavaScript this is really a simple example, which don’t need much to be understood. But in first place what is a stack?

You can thing of the “computer science” stack as a stack of sheets of paper, as it’s shown on the picture. You’ve three basic operations. You can add new element to the stack by putting it on the top of the stack, so the previous top of the stack becomes the second element in the stack. Another operation is to “pop” from the stack – remove the “first” element in the stack – the top most element, and to return it. And finally print the stack. This is difficult to define as an operation, but let say you’ve to show somehow every element from the stack.

Here’s a little diagram:

Stack

Source Code

At the end some source code:

var node = function()
{
    var data;
    var next = null;
}
 
var stack = function()
{
    this.top = null;
 
    this.push = function(data) {
        if (this.top == null) {
            this.top = new node();
            this.top.data = data;
        } else {
            var temp = new node();
            temp.data = data;
            temp.next = this.top;
            this.top = temp;
        }
    }
 
    this.pop = function() {
        var temp = this.top;
        var data = this.top.data;
        this.top = this.top.next;
        temp = null;
        return data;
    }
 
    this.print = function() {
        var node = this.top;
        while (node != null) {
            console.log(node.data);
            node = node.next;
        }
    }
}
 
var s = new stack();
 
s.push(1);
s.push(2);
s.push(3);
 
s.print();
 
var a = s.pop();
 
s.print();

Media RSS and ZF – Part 2

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Here’s the promised chunk of code making the most simple bridge between Zend Framework and Media RSS.

Step 1

Just add a simple action in a controller:

class IndexController extends Zend_Controller_Action
{
	public function indexAction()
	{
	    $this->getResponse()->setHeader('Content-Type', 'application/xml');
	    $this->view->somevar = 'some value';
 
	    echo $this->view->render('index/index.xml');
 
	    $this->_helper->layout()->disableLayout();
	    $this->_helper->viewRenderer->setNoRender(true);
	}
}

Step 2

After you’ve setup the xml file as a view script – you can simply access it as a normal Zend Framework view:

<rss version="2.0" xmlns:media="http://search.yahoo.com/mrss/" xmlns:av="http://www.searchvideo.com/schemas/av/1.0">
  <channel>
   <title><?php echo $this->somevar ?></title>
   ...
   other media rss elements
   ...
</channel>
</rss>

Default Error Handling in Zend Framework

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Zend_Controller_Action_Exception

There’s a cool feature in Zend Framework when a controller or action doesn’t exists. That’s really useful, because you simply write an ErrorController.php in you default module and every action’s exception sends the user to this controller/action and the job is done for you. What is important here is to show the error message at least on the development stage. Actually the request stores it as a parameter. Here’s some source:

<?php
 
class ErrorController extends Zend_Controller_Action
{
    public function errorAction()
    {
        $errorHandler = $this->getRequest()->getParam('error_handler');
        /* @var $error Zend_Controller_Action_Exception */
        $error = $errorHandler->exception;
        echo $error->getMessage();
    }
}

Zend Framework: Simple Acl Front Controller Plugin

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access with Zend_Acl

Almost every web site need some abstraction over the access control list (ACL) to grant access of its users. As usual Zend Framework has quite good mechanism to deal with this – Zend_Acl.

Out in the web there are a lot of resources about Zend_Acl’s usage, so I ain’t going to cover it one more time, but simply copy/paste a very small front controller plugin implementing the basic usage of Zend_Acl.

Note that instead of defining the __construct() here is called preDispatch where the request is passed as a parameter. However only by copy pasting not every answer will be given. That’s why I’m going to write more about Zend_Acl in my future posts, for now only the source code:

<?php
 
class AclInit extends Zend_Controller_Plugin_Abstract
{
    public function preDispatch(Zend_Controller_Request_Abstract $request)
    {
        // create new acl object
        $acl = new Zend_Acl();
 
        // define resources. typically there are
        // only four resources from the CRUD functionality
        // but there can be added more resources
        $acl->add(new Zend_Acl_Resource('index'))
            ->add(new Zend_Acl_Resource('create'))
            ->add(new Zend_Acl_Resource('read'))
            ->add(new Zend_Acl_Resource('update'))
            ->add(new Zend_Acl_Resource('delete'));
 
        // define roles
        $acl->addRole(new Zend_Acl_Role('guest'))
            ->addRole(new Zend_Acl_Role('admin'));
 
        // define privileges
        $acl->allow('guest', array('index', 'read'))
            ->allow('admin');
 
        // setup acl in the registry for more
        Zend_Registry::set('acl', $acl);
 
        // check permissions
        if (!$acl->isAllowed('guest', $request->getActionName())) {
            $request->setControllerName('error');
            $request->setActionName('error');
        }
    }
}