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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:
1 namespace MyProject\Entities;
use Doctrine\ORM\Mapping AS ORM;
use Symfony\Component\Validation\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;
}
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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:
1 use Doctrine\Common\Annotations\AnnotationReader;
use Doctrine\Common\Annotations\AnnotationRegistry;
AnnotationRegistry::registerFile("/path/to/doctrine/lib/Doctrine/ORM/Mapping/Driver/DoctrineAnnotations.php");
AnnotationRegistry::registerAutoloadNamespace("Symfony\Component\Validator\Constraint", "/path/to/symfony/src");
AnnotationRegistry::registerAutoloadNamespace("MyProject\Annotations", "/path/to/myproject/src");
$reader = new AnnotationReader();
AnnotationReader::addGlobalIgnoredName('dummy');
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The second block with the annotation registry calls registers all the
three different annotation namespaces that are used.
Doctrine Annotations saves all its annotations in a single file, that is
why AnnotationRegistry#registerFile
is used in contrast to
AnnotationRegistry#registerAutoloadNamespace
which creates a PSR-0
compatible loading mechanism for class to file names.
In the third block, we create the actual AnnotationReader
instance.
Note that we also add dummy
to the global list of ignored
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:
1 $reader = new \Doctrine\Common\Annotations\AnnotationReader();
This creates a simple annotation reader with no caching other than in memory (in php arrays). Since parsing docblocks can be expensive you should cache this process by using a caching reader.
You can use a file caching reader, but please note it is deprecated to do so:
If you set the debug
flag to true
the cache reader will check
for changes in the original files, which is very important during
development. If you don't set it to true
you have to delete the
directory to clear the cache. This gives faster performance, however
should only be used in production, because of its inconvenience during
development.
You can also use one of the Doctrine\Common\Cache\Cache
cache
implementations to cache the annotations:
The debug
flag is used here as well to invalidate the cache files
when the PHP class with annotations changed and should be used during
development.
By default the annotation reader returns a list of annotations with
numeric indexes. If you want your annotations to be indexed by their
class name you can wrap the reader in an IndexedReader
:
You should never wrap the indexed reader inside a cached reader, only the other way around. This way you can re-use the cache with indexed or numeric keys, otherwise your code may experience failures due to caching in a numerical or indexed format. |
Registering Annotations
As explained in the introduction, Doctrine Annotations uses its own
autoloading mechanism to determine if a given annotation has a
corresponding PHP class that can be autoloaded. For annotation
autoloading you have to configure the
Doctrine\Common\Annotations\AnnotationRegistry
. There are three
different mechanisms to configure annotation autoloading:
- Calling
AnnotationRegistry#registerFile($file)
to register a file that contains one or more annotation classes. - Calling `
AnnotationRegistry#registerNamespace($namespace, $dirs = null)
` to register that the given namespace contains annotations and that their base directory is located at the given $dirs or in the include path ifNULL
is passed. The given directories should NOT be the directory where classes of the namespace are in, but the base directory of the root namespace. The AnnotationRegistry uses a namespace to directory separator approach to resolve the correct path. - Calling
AnnotationRegistry#registerLoader($callable)
to register an autoloader callback. The callback accepts the class as first and only parameter and has to returntrue
if the corresponding file was found and included.
Loaders 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. |
A sample loader callback could look like:
1 use Doctrine\Common\Annotations\AnnotationRegistry;
use Symfony\Component\ClassLoader\UniversalClassLoader;
AnnotationRegistry::registerLoader(function($class) {
$file = str_replace("\\", DIRECTORY_SEPARATOR, $class) . ".php";
if (file_exists("/my/base/path/" . $file)) {
// file_exists() makes sure that the loader fails silently
require "/my/base/path/" . $file;
}
});
$loader = new UniversalClassLoader();
AnnotationRegistry::registerLoader(array($loader, "loadClass"));
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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:
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 can you 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: