98 lines
2.9 KiB
Markdown
98 lines
2.9 KiB
Markdown
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# Null Object Proxy
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A Null Object proxy is a [null object pattern](http://en.wikipedia.org/wiki/Null_Object_pattern) implementation.
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The proxy factory creates a new object with defined neutral behaviour based on another object, class name or interface.
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## What is null object proxy?
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In your application, when you cannot return the object related to the request, the consumer of the model must check for the
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return value and handle the failing condition gracefully, thus generating an explosion of conditionals throughout your code.
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Fortunately, this seemingly-tangled situation can be simplified by creating a polymorphic implementation of the domain object,
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which would implement the same interface as one of the objects in question, only that its methods would not do anything,
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therefore offloading client code from doing repetitive checks for ugly null values when the operation is executed.
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## Usage examples
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```php
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class UserMapper
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{
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private $adapter;
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public function __construct(DatabaseAdapterInterface $adapter) {
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$this->adapter = $adapter;
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}
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public function fetchById($id) {
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$this->adapter->select('users', ['id' => $id]);
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if (!$row = $this->adapter->fetch()) {
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return null;
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}
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return $this->createUser($row);
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}
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private function createUser(array $row) {
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$user = new Entity\User($row['name'], $row['email']);
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$user->setId($row['id']);
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return $user;
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}
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}
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```
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If you want to remove conditionals from client code, you need to have a version of the entity conforming to the corresponding
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interface. With the Null Object Proxy, you can build this object :
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```php
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$factory = new \ProxyManager\Factory\NullObjectFactory();
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$nullUser = $factory->createProxy('Entity\User');
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var_dump($nullUser->getName()); // empty return
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```
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You can now return a valid entity :
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```php
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class UserMapper
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{
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private $adapter;
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public function __construct(DatabaseAdapterInterface $adapter) {
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$this->adapter = $adapter;
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}
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public function fetchById($id) {
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$this->adapter->select('users', ['id' => $id]);
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return $this->createUser($this->adapter->fetch());
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}
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private function createUser($row) {
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if (!$row) {
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$factory = new \ProxyManager\Factory\NullObjectFactory();
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return $factory->createProxy('Entity\User');
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}
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$user = new Entity\User($row['name'], $row['email']);
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$user->setId($row['id']);
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return $user;
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}
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}
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```
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## Proxying interfaces
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You can also generate proxies from an interface FQCN. By proxying an interface, you will only be able to access the methods
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defined by the interface itself, and like with the object, the methods are empty.
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## Tuning performance for production
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See [Tuning ProxyManager for Production](tuning-for-production.md).
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