PHP Classes
elePHPant
Icontem

Building an Identity Map in PHP: Retrieve objects avoiding multiple instances

Recommend this page to a friend!
Stumble It! Stumble It! Bookmark in del.icio.us Bookmark in del.icio.us
  Info   View files View files (23)   DownloadInstall with Composer Download .zip   Reputation   Support forum (1)   Blog    
Last Updated Ratings Unique User Downloads Download Rankings  
2012-10-01 (2 years ago) RSS 2.0 feedNot enough user ratingsTotal: 441 All time: 5,757 This week: 1,336Up
Version License PHP version Categories  
php-identity-map 1BSD License5.0PHP 5, Databases, Design Patterns
Description Author  

This package can store and retrieve objects in persistent storage containers avoiding to have multiple instances of the same object in memory.

It can use a mapper class to store objects of a class in a container like for instance a database table.

It can also retrieve the objects from the container assuring that only one instance of the same object is retrieved into memory.

Picture of Gjero Krsteski
Name: Gjero Krsteski <contact>
Classes: 3 packages by
Country: Germany Germany
Age: 35
All time rank: 1833118 in Germany Germany
Week rank: 1460 Up72 in Germany Germany Up
Innovation award
Innovation award
Nominee: 1x

Details provided by the author  
Building an Identity Map in PHP
===============================

Sample application used for training.

This example code is no production code and should be used for training
purposes only.

This example code requires:
---------------------------
* PDO a lightweight, consistent interface for accessing databases in PHP.
* PHPUnit a unit testing framework for PHP projects.

This example code implements:
-----------------------
* Data-Mapper Pattern
* Identity-Map Pattern

Why identity mapping?
---------------------
By using Data-Mapper pattern without an identity map, you can easily run
into problems because you may have more than one object that references
the same domain entity.

Data-Mapper without identity map
----------------------------------

      $userMapper = new UserMapper($pdo);

      $user1 = $userMapper->find(1); // creates new object
      $user2 = $userMapper->find(1); // creates new object

      echo $user1->getNickname(); // joe123
      echo $user2->getNickname(); // joe123

      $user1->setNickname('bob78');

      echo $user1->getNickname(); // bob78
      echo $user2->getNickname(); // joe123 -> ?!?

Data-Mapper with identity map
----------------------------------
The identity map solves this problem by acting as a registry for all
loaded domain instances.

      $userMapper = new UserMapper($pdo);

      $user1 = $userMapper->find(1); // creates new object
      $user2 = $userMapper->find(1); // returns same object

      echo $user1->getNickname(); // joe123
      echo $user2->getNickname(); // joe123

      $user1->setNickname('bob78');

      echo $user1->getNickname(); // bob78
      echo $user2->getNickname(); // bob78 -> yes, much better

By using an identity map you can be confident that your domain entity is
shared throughout your application for the duration of the request.

Note that using an identity map is not the same as adding a cache layer
to your mappers. Although caching is useful and encouraged, it can still
produce duplicate objects for the same domain entity.

Load the Data-Mappers with the Repository class
-----------------------------------------------


      $repository = new Repository($this->db);
      $userMapper = $repository->load('User');
      $insertId = $userMapper->insert(new User('billy', 'gatter'));
      
  Files folder image Files  
File Role Description
Files folder imagedatabase (2 files)
Files folder imagesrc (1 file, 3 directories)
Files folder imagetests (1 file, 2 directories)
Plain text file autoload.php Class autoloder
Accessible without login Plain text file phpunit.xml.dist Data phpunit configuration
Accessible without login Plain text file README.markdown Doc. README
Accessible without login Plain text file test-bootstrap.php Aux. bootstraping
Accessible without login Image file uml-php-identity-map.gif Data Auxiliary data

  Files folder image Files  /  database  
File Role Description
  Accessible without login Plain text file tbl_article.sql Data Auxiliary data
  Accessible without login Plain text file tbl_user.sql Data Auxiliary data

  Files folder image Files  /  src  
File Role Description
Files folder imageframework (3 files)
Files folder imagemodel (2 files)
Files folder imagepersistence (3 files)
  Plain text file Repository.php Class Class source

  Files folder image Files  /  src  /  framework  
File Role Description
  Plain text file IdentityMap.php Class the indentity-map
  Plain text file MapperException.php Class mapper exception
  Plain text file RecursiveClassLoder.php Class Class source

  Files folder image Files  /  src  /  model  
File Role Description
  Plain text file Article.php Class Class source
  Plain text file User.php Class the user model

  Files folder image Files  /  src  /  persistence  
File Role Description
  Plain text file AbstractMapper.php Class Class source
  Plain text file ArticleMapper.php Class Class source
  Plain text file UserMapper.php Class the user mapper

  Files folder image Files  /  tests  
File Role Description
Files folder imagemodel (2 files)
Files folder imagepersistence (2 files, 1 directory)
  Plain text file RepositoryTest.php Class Class source

  Files folder image Files  /  tests  /  model  
File Role Description
  Plain text file ArticleTest.php Class Class source
  Accessible without login Plain text file UserTest.php Test user model test

  Files folder image Files  /  tests  /  persistence  
File Role Description
Files folder imagefixture (2 files)
  Plain text file ArticleMapperTest.php Class Class source
  Accessible without login Plain text file UserMapperTest.php Test UserMapperTest

  Files folder image Files  /  tests  /  persistence  /  fixture  
File Role Description
  Accessible without login Plain text file article-seed.xml Data Auxiliary data
  Accessible without login Plain text file user-seed.xml Data user-seed

 Version Control Unique User Downloads Download Rankings  
 100%Total:441All time:5,757
 This week:0This week:1,336Up
 User Comments (1)