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null-object.md
01 # Null Object Proxy
02
03 A Null Object proxy is a [null object pattern](http://en.wikipedia.org/wiki/Null_Object_pattern) implementation.
04 The proxy factory creates a new object with defined neutral behavior based on an other object, class name or interface.
05
06 ## What is null object proxy ?
07
08 In your application, when you can't return the object related to the request, the consumer of the model must check
09 for the return value and handle the failing condition gracefully, thus generating an explosion of conditionals throughout your code.
10 Fortunately, this seemingly-tangled situation can be sorted out simply by creating a polymorphic implementation of the
11 domain object, which would implement the same interface as the one of the object in question, only that its methods
12 wouldn’t do anything, therefore offloading client code from doing repetitive checks for ugly null values when the operation
13 is executed.
14
15 ## Usage examples
16
17 ```php
18 class UserMapper
19 {
20 private $adapter;
21
22 public function __construct(DatabaseAdapterInterface $adapter) {
23 $this->adapter = $adapter;
24 }
25
26 public function fetchById($id) {
27 $this->adapter->select("users", array("id" => $id));
28 if (!$row = $this->adapter->fetch()) {
29 return null;
30 }
31 return $this->createUser($row);
32 }
33
34 private function createUser(array $row) {
35 $user = new Entity\User($row["name"], $row["email"]);
36 $user->setId($row["id"]);
37 return $user;
38 }
39 }
40 ```
41
42 If you want to remove conditionals from client code, you need to have a version of the entity conforming to the corresponding
43 interface. With the Null Object Proxy, you can build this object :
44
45 ```php
46 $factory = new \ProxyManager\Factory\NullObjectFactory();
47
48 $nullUser = $factory->createProxy('Entity\User');
49
50 var_dump($nullUser->getName()); // empty return
51 ```
52
53 You can now return a valid entity :
54
55 ```php
56 class UserMapper
57 {
58 private $adapter;
59
60 public function __construct(DatabaseAdapterInterface $adapter) {
61 $this->adapter = $adapter;
62 }
63
64 public function fetchById($id) {
65 $this->adapter->select("users", array("id" => $id));
66 return $this->createUser($this->adapter->fetch());
67 }
68
69 private function createUser($row) {
70 if (!$row) {
71 $factory = new \ProxyManager\Factory\NullObjectFactory();
72
73 return $factory->createProxy('Entity\User');
74 }
75 $user = new Entity\User($row["name"], $row["email"]);
76 $user->setId($row["id"]);
77 return $user;
78 }
79 }
80 ```
81
82 ## Proxying interfaces
83
84 You can also generate proxies from an interface FQCN. By proxying an interface, you will only be able to access the
85 methods defined by the interface itself, and like with the object, the methods are empty.
86
87 ## Tuning performance for production
88
89 See [Tuning ProxyManager for Production](https://github.com/Ocramius/ProxyManager/blob/master/docs/tuning-for-production.md).
90