Data Mapper Design Pattern Complete Example

DataMapperTest.php

<?php

namespace DPatterns;

use \DPatterns\PostMemoryStorage;
use \DPatterns\Post;
use \DPatterns\PostMapper;
use \PHPUnit\Framework\TestCase;

class DataMapperTest extends TestCase
{
	public function testCanMapUserFromStorage()
	{
		// instantiating data in the database
		$storage = new PostMemoryStorage([1 => ['post_name' => 'orm', 'post_body' => 'Learning Orm']]);

		// Mapping Layer
		$mapper = new PostMapper( $storage );

		$post = $mapper->find_by_id(1);

		$this->assertInstanceOf(Post::class, $post);
	}

	/**
	 * @expectedException \InvalidArgumentException
	 */
	public function testWillNotMapInvalidData()
	{
		$storage = new PostMemoryStorage([]);

		$mapper = new PostMapper( $storage );

		$mapper->find_by_id( 5 );
	}
}

PersistenceStorage.php

<?php namespace DPatterns;

interface PersistenceStorage {

	public function find( int $id );

}

Post.php

<?php namespace DPatterns ;

/**
 * Class Post
 * Our Post Class Which we specify Post attributes
 *
 * @package DPatterns
 */
class Post{

	protected $id ;

	protected $post_name ;

	protected $post_body ;

	function __construct( $post_name , $post_body )
	{
		$this->post_name = $post_name ;
		$this->post_body = $post_body ;
	}

	public static function create_from_state( $state ) : Post
	{
		return new self(
			$state['post_name'],
			$state['post_body']
		);
	}

	/**
	 * @return mixed
	 */
	public function getId()
	{
		return $this->id;
	}

	/**
	 * @return mixed
	 */
	public function getPostName()
	{
		return $this->post_name;
	}

	/**
	 * @param mixed $post_name
	 */
	public function setPostName($post_name)
	{
		$this->post_name = $post_name;
	}

	/**
	 * @return mixed
	 */
	public function getPostBody()
	{
		return $this->post_body;
	}

	/**
	 * @param mixed $post_body
	 */
	public function setPostBody($post_body)
	{
		$this->post_body = $post_body;
	}

}

PostMapper.php

<?php namespace DPatterns ;

use DPatterns\PersistenceStorage ;
use DPatterns\Post ;

class PostMapper{

	protected $PersistenceStorage ;

	/**
	 * PostMapper constructor.
	 * @Demonstration_for_learning
	 * * Whatever The Persistence Storage Method you use it must implement the Interface PersistenceStorage
	 * * which Ensures Consistency Across All Storage Methods Used .
	 *
	 * @param PersistenceStorage $PersistenceStorage
	 */
	function __construct( PersistenceStorage $PersistenceStorage )
	{
		$this->PersistenceStorage = $PersistenceStorage ;
	}

	public function find_by_id( int $id )
	{
		$result = $this->PersistenceStorage->find( $id );

		if( is_null( $result ) ){
			throw new \InvalidArgumentException("Post #$id not found");
		}

		return $this->mapRowToPost( $result );
	}

	private function mapRowToPost( $post ){
		return Post::create_from_state( $post );
	}
}

PostMemoryStorage.php

<?php namespace DPatterns ;

use DPatterns\PersistenceStorage ;

/**
 * Class PostMemoryStorage
 * For Simplicity We will make it in memory data store
 *
 * @package DPatterns
 */
class PostMemoryStorage implements PersistenceStorage{

	private $data = [] ;

	function __construct( array $data )
	{
		$this->data = $data;
	}

	/**
	 * @param int $id
	 * @return mixed|null
	 */
	public function find( int $id )
	{
		if ( isset( $this->data[$id] ) ) {
			return $this->data[$id];
		}

		return null;
	}

}