Zend Framework DAL: DAOs and DataMappers

A Data Access Layer (DAL) is the layer of your application that provides simplified access to data stored in persistent storage of some kind. For example, the DAL might return a reference to an object complete with its attributes instead of a row of fields from a database table.

A Data Access Objects (DAO) is used to abstract and encapsulate all access to the data source. The DAO manages the connection with the data source to obtain and store data. Also, it implements the access mechanism required to work with the data source. The data source could be a persistent store like a database, a file or a Web service.

And finally, the DataMapper pattern is used to move data between the object and a database while keeping them independent of each other. The DataMapper main responsibility is to transfer data between the two and also to isolate them from each other.

Here’s an example of the DataMapper pattern:

Database Table Structure

CREATE TABLE `user` (
 `id` int(11) NOT NULL auto_increment,
 `first_name` varchar(100) NOT NULL,
 `last_name` varchar(100) NOT NULL,
 PRIMARY KEY  (`id`)
)

The User DAO

The DAO pattern provides a simple, consistent API for data access that does not require knowledge of an ORM interface. DAO does not just apply to simple mappings of one object to one relational table, but also allows complex queries to be performed and allows for stored procedures and database views to be mapped into data structures.

A typical DAO design pattern interface is shown below:

interface UserDao
{
    public function fetchRow($id);
    public function fetchAll();
    public function insert($data);
    public function update($id, $data);
    public function delete($id);
}

class UserDatabaseDao implements UserDao
{
    public function fetchRow($id)
    {
        $dataSource = Zf_Orm_Manager::getInstance()->getDataSource();
        $db = $dataSource->getConnection('slave');
        $query = $db->select()->from('user')->where('id = ?', $id);
        return $db->fetchRow($query);
    }

    public function fetchAll()
    {
        $dataSource = Zf_Orm_Manager::getInstance()->getDataSource();
        $db = $dataSource->getConnection('slave');
        $query = $db->select()->from('user');
        return $db->fetchAll($query);
    }

    public function insert($data)
    {
        $dataSource = Zf_Orm_Manager::getInstance()->getDataSource();
        $db = $dataSource->getConnection('master');
        $db->insert('user', $data);
        return $db->lastInsertId();
    }

    public function update($id, $data)
    {
        $dataSource = Zf_Orm_Manager::getInstance()->getDataSource();
        $db = $dataSource->getConnection('master');
        $condition = $db->quoteInto('id = ?', $id);
        return $db->update('user', $data, $condition);
    }

    public function delete($id)
    {
        $dataSource = Zf_Orm_Manager::getInstance()->getDataSource();
        $db = $dataSource->getConnection('master');
        $condition = $db->quoteInto('id = ?', $id);
        return $db->delete('user', $condition);
    }
}

The User Entity

An Entity is anything that has continuity through a life cycle and distinctions independent of attributes that are important to the application’s user.

class User
{
    protected $id;
    protected $firstName;
    protected $lastName;

    public function setId() {
    }
    public function getId() {
    }
    public function setFirstName() {
    }
    public function getFirstName() {
    }
    public function setLastName() {
    }
    public function getLastName() {
    }
    public function toArray() {
    }
}

The User DataMapper

class UserDataMapper extends Zf_Orm_DataMapper
{
    public function __construct()
    {
        $this->setMap(
            array(
                'id'         => 'id',
                'first_name' => 'firstName',
                'last_name'  => 'lastName'
            )
        );
    }
}

Source Code: http://fedecarg.com/repositories/show/datamapper

The User Repository

Repositories play an important part in DDD, they speak the language of the domain and act as mediators between the domain and data mapping layers. They provide a common language to all team members by translating technical terminology into business terminology.

Lets create a UserRepository class to isolate the domain object from details of the DAO:

class UserRepository
{
    private $databaseDao;

    public funciton setDatabaseDao(UserDao $dao)
    {
        $this->databaseDao = $dao;
    }

    public function getDatabaseDao()
    {
        if (null === $this->databaseDao) {
            $this->setDatabaseDao(new UserDatabaseDao());
        }
        return $this->databaseDao;
    }

    public function find($id)
    {
        $row = $this->getDatabaseDao()->fetchRow($id);
        $mapper = new UserDataMapper();
        $user = $mapper->assign(new User(), $row);

        return $user;
    }
}

The User Controller

class UserController extends Zend_Controller_Action
{
    public function viewAction()
    {
        $userRepository = new UserRepository();
        $user = $userRepository->find($this->_getParam('id'));
        if ($user instanceof User) {
            $id = $user->getId();
            $firstName = $user->getFirstName();
            $lastName = $user->getLastName();
            // get an array of key value pairs
            $row = $user->toArray();
        }
    }
}

That’s all, I hope you’ve found this post useful.

Towards Community Cloud Computing

Cloud Computing is rising fast, with its data centers growing at an unprecedented rate. However, this has come with concerns of privacy, efficiency at the expense of resilience, and environmental sustainability, because of the dependence on Cloud vendors such as Google, Amazon, and Microsoft. Community Cloud Computing makes use of the principles of Digital Ecosystems to provide a paradigm for Clouds in the community, offering an alternative architecture for the use cases of Cloud Computing. It is more technically challenging to deal with issues of distributed computing, such as latency, differential resource management, and additional security requirements. However, these are not insurmountable challenges, and with the need to retain control over our digital lives and the potential environmental consequences, it is a challenge we must pursue.

Towards Community Cloud Computing (Visit Site | Download PDF)

Java, C, Python and nested loops

Java has no goto statement, to break or continue multiple-nested loop or switch constructs, Java programmers place labels on loop and switch constructs, and then break out of or continue to the block named by the label. The following example shows how to use java break statement to terminate the labeled loop:

public class BreakLabel
{
    public static void main(String[] args)
    {
        int[][] array = new int[][]{{1,2,3,4},{10,20,30,40}};
        boolean found = false;
        System.out.println("Searching 30 in two dimensional int array");

        Outer:
        for (int intOuter = 0; intOuter < array.length ; intOuter++) {
            Inner:
            for (int intInner = 0; intInner < array[intOuter].length; intInner++) {
                if (array[intOuter][intInner] == 30) {
                    found = true;
                    break Outer;
                }
            }
        }

        if (found == true) {
            System.out.println("30 found in the array");
        } else {
            System.out.println("30 not found in the array");
        }
    }
}

Use of labeled blocks in Java leads to considerable simplification in programming effort and a major reduction in maintenance.

On the other hand, the C continue statement can only continue the immediately enclosing block; to continue or exit outer blocks, programmers have traditionally either used auxiliary Boolean variables whose only purpose is to determine if the outer block is to be continued or exited; alternatively, programmers have misused the goto statement to exit out of nested blocks.

What’s interesting is that Python rejected the labeled break and continue proposal a while ago. And here’s why:

Guido van Rossum wrote:

I’m rejecting it on the basis that code so complicated to require this feature is very rare. While I’m sure there are some (rare) real cases where clarity of the code would suffer from a refactoring that makes it possible to use return, this is offset by two issues:

1. The complexity added to the language, permanently.

2. My expectation that the feature will be abused more than it will be used right, leading to a net decrease in code clarity (measured across all Python code written henceforth). Lazy programmers are everywhere, and before you know it you have an incredible mess on your hands of unintelligible code.

But what’s more interesting is that the idea of adding a goto statement was never mentioned. Common sense perhaps?

The Cost of Hosting on Amazon

Mather Corgan, president of HotPads, gave a great talk on how HotPads uses AWS to run their real estate search engine. HotPads abandoned their managed hosting in December and took the leap over to EC2 and its siblings. The presentation has a lot of detail on costs and other things to watch out for, so if you’re currently planning your “cloud” architecture, you’ll find some of this really helpful.

HotPads on AWS

The Little Manual of API Design

This manual gathers together the key insights into API design that were discovered through many years of software development on the Qt application development framework at Trolltech (now part of Nokia). When designing and implementing a library, you should also keep other factors in mind, such as efficiency and ease of implementation, in addition to pure API considerations. And although the focus is on public APIs, there is no harm in applying the principles described here when writing application code or internal library code.

The Little Manual of API Design (PDF)

An Alternative to Zend_Controller

Zend Framework is very flexible and one of its strengths is that it allows developers to implement their own components. The Zend_Controller component, for example, is very powerful. Of course, it’s not my intention to replace it, but to offer an alternative that decreases the number of decisions a developer needs to make when developing an application.

Meet Zf_Controller. The Zf_Controller component has the following goals:

  • Abstract complexity: Try to reduce the level of details so the developer can focus on a few concepts at a time.
  • Emphasize Convention over Configuration: Emphasize CoC, meaning that the user only needs to specify unconventional aspects of the application.
  • Maintain backwards compatibility: Allow the developer to replace Zf_Controller with Zend_Controller in case the application grows in size or complexity.
  • Improve performance: Load less classes, execute less code.
  • Remove circular references: Avoid circular references.
  • Remove Singleton classes: Avoid implementing the Singleton pattern.
  • Research: Learn more about the framework, what it does, how it works.

Project Structure

Zend_Controller allows you to use the project structure that best suits your needs. On the other hand, Zf_Controller is more rigid, it only allows you to use the standard project structure:

project/
  app/
    config/
    controllers/
      ErrorController.php
      IndexController.php
    views/
      layouts/
      scripts/
        error/
        index/
          index.phtml
  domain/
    Model/
      Example.php
  lib/
    Zend/
    Zf/

Zf_Controller classes:

Zf/
  Controller/
    Action/
      Helper/
        Layout.php
    Action.php
    Front.php

Bootstrap File

Zend_Controller:

define('APPLICATION_PATH', realpath(dirname(__FILE__) . '/../app'));
set_include_path(APPLICATION_PATH . '/../lib'
    . PATH_SEPARATOR . get_include_path());

require_once "Zend/Loader.php";
Zend_Loader::registerAutoload();

$frontController = Zend_Controller_Front::getInstance();
$router = $frontController->getRouter();
$routes = include_once APPLICATION_PATH . '/config/routes.php';
$router->addRoutes($routes);

$layout = Zend_Layout::startMvc();
$layout->setLayoutPath(APPLICATION_PATH . '/views/layouts');

$frontController->dispatch();

Zf_Controller (no Router):

define('APPLICATION_PATH', realpath(dirname(__FILE__) . '/../app'));
set_include_path(APPLICATION_PATH . '/../lib'
    . PATH_SEPARATOR . APPLICATION_PATH . '/../domain);

require_once "Zend/Loader.php";
Zend_Loader::registerAutoload();

$frontController = new Zf_Controller_Front();
$frontController->setLayoutPath(APPLICATION_PATH . '/views/layouts');
$frontController->dispatch();

Action Controller

The default action controller and the default action are named “index”:

class IndexController extends Zf_Controller_Action
{
  public function indexAction()
  {}
}

Error Controller

Zend_Controller:

class ErrorController extends Zend_Controller_Action
{
  // Action used by Zend_Controller
  public function errorAction()
  {
    $error = $this->_getParam('error_handler');
    echo $error->exception->getMessage();
  }
}

Zf_Controller:

class ErrorController extends Zf_Controller_Action
{
  // Action used by Zf_Controller
  public function indexAction($e)
  {
    echo $e->getMessage();
  }
}

Rendering a View Script

Zf_Controller does not use the ViewRenderer helper class. To make the code more readable and testable, you need to call the render() method and return a value:

class IndexController extends Zf_Controller_Action
{
  public function indexAction()
  {
    $view = $this->initView();
    $view->message = 'Hello';

    // Renders views/scripts/index/index.phtml
    return $this->render();
  }

  public function testAction()
  {
    $view = $this->initView();
    $view->message = 'Goodbye';

    // Renders views/scripts/index/index.phtml
    return $this->render('index');
  }}

index.phtml file:

<p><?php echo $this->message ?></p>

Using a Layout

By setting the path to your layouts in the Bootstrap file, you automatically enable the default layout “layout.phtml”:

$frontController = new Zf_Controller_Front();
$frontController->setLayoutPath(APPLICATION_PATH . '/views/layouts');

To disable the layout:

class IndexController extends Zf_Controller_Action
{
    protected $_isLayoutEnabled = false;
}

To use a different layout:

class IndexController extends Zf_Controller_Action
{
    protected $_layoutScript = 'main.phtml';
}

main.phtml file:

<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<?php echo $this->headTitle() ?>
<?php echo $this->headScript() ?>
<?php echo $this->headStyle() ?>
</head>
<body>
<div id="content"><?php echo $this->layout()->content ?></div>
</body>
</html>

Source Code:
http://svn.fedecarg.com/repo/Zf/Controller/

Implementing your own Front Controller in Zend Framework

There’s no doubt that the additional complexity of implementing the default Front Controller in ZF results in a number of benefits. The most important ones are flexibility and extensibility. The Front Controller implementation takes into consideration the future growth of your application and its design reduces the level of effort required to extend it. A good example of this is the plugin architecture.

But, what if after evaluating the requirements of your system, you determine that there’s not sufficient complexity to implement the default Front Controller? What if you don’t need all that flexibility, a URL mapper, a ViewRendered plugin or an ActionStack helper. Maybe all you need is just a couple of controllers, and that’s it. It’s clear that the standard Front Controller does provide more options and meets every possible use case requirement, but at the cost of complexity and a lot of classes.

So, what to do? Do you choose a different tool for the job, or replace the default Front Controller with your own implementation? How hard can it be? Is it really that difficult to replace the most important component of the Zend Framework and maintain backwards compatibility?

You are about to find out.

In this series of posts, I’ll try to cover a few things I’ve learned about implementing my own Front Controller in Zend Framework. Most of the ideas and code are based on my previous posts:

Will simplicity finally meet power?