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Handling Annotations

There are several different approaches to handling annotations in PHP. Doctrine Annotations maps docblock annotations to PHP classes. Because not all docblock annotations are used for metadata purposes a filter is applied to ignore or skip classes that are not Doctrine annotations.

Take a look at the following code snippet:

namespace MyProject\Entities;

use Doctrine\ORM\Mapping AS ORM;
use Symfony\Component\Validator\Constraints AS Assert;

/**
 * @author Benjamin Eberlei
 * @ORM\Entity
 * @MyProject\Annotations\Foobarable
 */
class User
{
    /**
     * @ORM\Id @ORM\Column @ORM\GeneratedValue
     * @dummy
     * @var int
     */
    private $id;

    /**
     * @ORM\Column(type="string")
     * @Assert\NotEmpty
     * @Assert\Email
     * @var string
     */
    private $email;
}

In this snippet you can see a variety of different docblock annotations:

  • Documentation annotations such as @var and @author. These annotations are on a blacklist and never considered for throwing an exception due to wrongly used annotations.
  • Annotations imported through use statements. The statement use Doctrine\ORM\Mapping AS ORM makes all classes under that namespace available as @ORM\ClassName. Same goes for the import of @Assert.
  • The @dummy annotation. It is not a documentation annotation and not blacklisted. For Doctrine Annotations it is not entirely clear how to handle this annotation. Depending on the configuration an exception (unknown annotation) will be thrown when parsing this annotation.
  • The fully qualified annotation @MyProject\Annotations\Foobarable. This is transformed directly into the given class name.

How are these annotations loaded? From looking at the code you could guess that the ORM Mapping, Assert Validation and the fully qualified annotation can just be loaded using the defined PHP autoloaders. This is not the case however: For error handling reasons every check for class existence inside the AnnotationReader sets the second parameter $autoload of class_exists($name, $autoload) to false. To work flawlessly the AnnotationReader requires silent autoloaders which many autoloaders are not. Silent autoloading is NOT part of the PSR-0 specification for autoloading.

This is why Doctrine Annotations uses its own autoloading mechanism through a global registry. If you are wondering about the annotation registry being global, there is no other way to solve the architectural problems of autoloading annotation classes in a straightforward fashion. Additionally if you think about PHP autoloading then you recognize it is a global as well.

To anticipate the configuration section, making the above PHP class work with Doctrine Annotations requires this setup:

use Doctrine\Annotations\AnnotationReader;

$reader = new AnnotationReader();
AnnotationReader::addGlobalIgnoredName('dummy');

In the second block, we create the actual AnnotationReader instance. Note that we also add "dummy" to the global list of annotations for which we do not throw exceptions. Setting this is necessary in our example case, otherwise @dummy would trigger an exception to be thrown during the parsing of the docblock of MyProject\Entities\User#id.

Setup and Configuration

To use the annotations library is simple, you just need to create a new AnnotationReader instance:

$reader = new \Doctrine\Annotations\AnnotationReader();

This creates a simple annotation reader with no caching other than in memory (in php arrays). Since parsing docblocks can be expensive you should cache this process by using a caching reader.

You can use one of the Doctrine\Common\Cache\Cache cache implementations to cache the annotations:

use Doctrine\Annotations\AnnotationReader;
use Doctrine\Annotations\CachedReader;
use Doctrine\Common\Cache\ApcCache;

$reader = new CachedReader(
    new AnnotationReader(),
    new ApcCache(),
    $debug = true
);

The debug flag is used here to invalidate the cache files when the PHP class with annotations changed and should be used during development.

The AnnotationReader works and caches under the assumption that all annotations of a doc-block are processed at once. That means that annotation classes that do not exist and aren't loaded and cannot be autoloaded would never be visible and not accessible if a cache is used unless the cache is cleared and the annotations requested again, this time with all annotations defined.

By default the annotation reader returns a list of annotations with numeric indexes. If you want your annotations to be indexed by their class name you can wrap the reader in an IndexedReader:

use Doctrine\Annotations\AnnotationReader;
use Doctrine\Annotations\IndexedReader;

$reader = new IndexedReader(new AnnotationReader());

You should never wrap the indexed reader inside a cached reader only the other way around. This way you can re-use the cache with indexed or numeric keys, otherwise your code may experience failures due to caching in an numerical or indexed format.

Registering Annotations

Doctrine Annotations rely on native PHP autoloading. Make sure your annotations are known by your autoloader.

Autoloaders have to fail silently, if a class is not found even if it matches for example the namespace prefix of that loader. Never is a loader to throw a warning or exception if the loading failed otherwise parsing doc block annotations will become a huge pain.

Ignoring missing exceptions

By default an exception is thrown from the AnnotationReader if an annotation was found that:

  • Is not part of the blacklist of ignored "documentation annotations".
  • Was not imported through a use statement
  • Is not a fully qualified class that exists

You can disable this behavior for specific names if your docblocks do not follow strict requirements:

$reader = new \Doctrine\Annotations\AnnotationReader();
AnnotationReader::addGlobalIgnoredName('foo');

PHP Imports

By default the annotation reader parses the use-statement of a php file to gain access to the import rules and register them for the annotation processing. Only if you are using PHP Imports you can validate the correct usage of annotations and throw exceptions if you misspelled an annotation. This mechanism is enabled by default.

To ease the upgrade path, we still allow you to disable this mechanism. Note however that we will remove this in future versions:

$reader = new \Doctrine\Annotations\AnnotationReader();
$reader->setEnabledPhpImports(false);