Sebastian Bergmann

The Object_Freezer library for PHP provides the low-level functionality to store ("freeze") and fetch ("thaw") any PHP userland object to and from arbitrary object stores.

Today I added an object storage implementation that uses Apache CouchDB as its backend.

Apache CouchDB, the distributed, fault-tolerant and schema-free document-oriented database that provides scalability as a consequence of its design, is a natural fit for such an object store.

The following example shows how the Object_Freezer's new backend for CouchDB can be used to persist PHP objects:

<?php
require 'Object/Freezer/Storage/CouchDB.php';
 
class Foo
{
    public $a;
    protected $b;
    private $c;
 
    public function __construct($a, $b, $c)
    {
        $this->a = $a;
        $this->b = $b;
        $this->c = $c;
    }
}
 
$object = new Foo(1, 2, 3);
var_dump($object);
 
// Store the object in the database "test" of the
// CouchDB server that is running on localhost:5984.
$storage = new Object_Freezer_Storage_CouchDB('test');
$storage->store($object);
 
// Freezing the object added the "magic" attributes
// __php_object_freezer_uuid and __php_object_freezer_hash.
var_dump($object);
 
// Fetch the object (by ID) from the database.
var_dump($storage->fetch($object->__php_object_freezer_uuid));
?>

Below is the output produced by the script above:

object(Foo)#1 (3) {
  ["a"]=>
  int(1)
  ["b":protected]=>
  int(2)
  ["c":"Foo":private]=>
  int(3)
}

object(Foo)#1 (5) {
  ["a"]=>
  int(1)
  ["b":protected]=>
  int(2)
  ["c":"Foo":private]=>
  int(3)
  ["__php_object_freezer_uuid"]=>
  string(36) "8d17b95e-1410-4e54-a70c-064c09c79210"
  ["__php_object_freezer_hash"]=>
  string(40) "40cd89ec4ea3b5a1c1419c83b4ea643da5341ab8"
}

object(Foo)#10 (5) {
  ["a"]=>
  int(1)
  ["b":protected]=>
  int(2)
  ["c":"Foo":private]=>
  int(3)
  ["__php_object_freezer_uuid"]=>
  string(36) "8d17b95e-1410-4e54-a70c-064c09c79210"
  ["__php_object_freezer_hash"]=>
  string(40) "40cd89ec4ea3b5a1c1419c83b4ea643da5341ab8"
}

Here is an overview of the current feature set:

• PHP objects, with the exception of objects of "special" classes such as Closure or PDO, can be frozen and thawed.
• Graphs of objects, including those that contain circular references, are supported.
• Frozen objects can be stored in and fetched from an Apache CouchDB database.