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vendor/doctrine/annotations/docs/en/annotations.rst
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vendor/doctrine/annotations/docs/en/annotations.rst
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Handling Annotations
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====================
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There are several different approaches to handling annotations in PHP.
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Doctrine Annotations maps docblock annotations to PHP classes. Because
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not all docblock annotations are used for metadata purposes a filter is
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applied to ignore or skip classes that are not Doctrine annotations.
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Take a look at the following code snippet:
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.. code-block:: php
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namespace MyProject\Entities;
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use Doctrine\ORM\Mapping AS ORM;
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use Symfony\Component\Validator\Constraints AS Assert;
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/**
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* @author Benjamin Eberlei
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* @ORM\Entity
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* @MyProject\Annotations\Foobarable
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*/
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class User
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{
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/**
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* @ORM\Id @ORM\Column @ORM\GeneratedValue
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* @dummy
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* @var int
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*/
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private $id;
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/**
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* @ORM\Column(type="string")
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* @Assert\NotEmpty
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* @Assert\Email
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* @var string
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*/
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private $email;
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}
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In this snippet you can see a variety of different docblock annotations:
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- Documentation annotations such as ``@var`` and ``@author``. These
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annotations are ignored and never considered for throwing an
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exception due to wrongly used annotations.
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- Annotations imported through use statements. The statement ``use
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Doctrine\ORM\Mapping AS ORM`` makes all classes under that namespace
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available as ``@ORM\ClassName``. Same goes for the import of
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``@Assert``.
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- The ``@dummy`` annotation. It is not a documentation annotation and
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not ignored. For Doctrine Annotations it is not entirely clear how
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to handle this annotation. Depending on the configuration an exception
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(unknown annotation) will be thrown when parsing this annotation.
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- The fully qualified annotation ``@MyProject\Annotations\Foobarable``.
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This is transformed directly into the given class name.
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How are these annotations loaded? From looking at the code you could
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guess that the ORM Mapping, Assert Validation and the fully qualified
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annotation can just be loaded using
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the defined PHP autoloaders. This is not the case however: For error
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handling reasons every check for class existence inside the
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``AnnotationReader`` sets the second parameter $autoload
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of ``class_exists($name, $autoload)`` to false. To work flawlessly the
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``AnnotationReader`` requires silent autoloaders which many autoloaders are
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not. Silent autoloading is NOT part of the `PSR-0 specification
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<https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md>`_
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for autoloading.
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This is why Doctrine Annotations uses its own autoloading mechanism
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through a global registry. If you are wondering about the annotation
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registry being global, there is no other way to solve the architectural
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problems of autoloading annotation classes in a straightforward fashion.
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Additionally if you think about PHP autoloading then you recognize it is
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a global as well.
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To anticipate the configuration section, making the above PHP class work
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with Doctrine Annotations requires this setup:
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.. code-block:: php
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use Doctrine\Common\Annotations\AnnotationReader;
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use Doctrine\Common\Annotations\AnnotationRegistry;
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AnnotationRegistry::registerFile("/path/to/doctrine/lib/Doctrine/ORM/Mapping/Driver/DoctrineAnnotations.php");
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AnnotationRegistry::registerAutoloadNamespace("Symfony\Component\Validator\Constraint", "/path/to/symfony/src");
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AnnotationRegistry::registerAutoloadNamespace("MyProject\Annotations", "/path/to/myproject/src");
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$reader = new AnnotationReader();
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AnnotationReader::addGlobalIgnoredName('dummy');
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The second block with the annotation registry calls registers all the
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three different annotation namespaces that are used.
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Doctrine Annotations saves all its annotations in a single file, that is
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why ``AnnotationRegistry#registerFile`` is used in contrast to
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``AnnotationRegistry#registerAutoloadNamespace`` which creates a PSR-0
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compatible loading mechanism for class to file names.
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In the third block, we create the actual ``AnnotationReader`` instance.
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Note that we also add ``dummy`` to the global list of ignored
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annotations for which we do not throw exceptions. Setting this is
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necessary in our example case, otherwise ``@dummy`` would trigger an
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exception to be thrown during the parsing of the docblock of
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``MyProject\Entities\User#id``.
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Setup and Configuration
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-----------------------
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To use the annotations library is simple, you just need to create a new
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``AnnotationReader`` instance:
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.. code-block:: php
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$reader = new \Doctrine\Common\Annotations\AnnotationReader();
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This creates a simple annotation reader with no caching other than in
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memory (in php arrays). Since parsing docblocks can be expensive you
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should cache this process by using a caching reader.
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To cache annotations, you can create a ``Doctrine\Common\Annotations\PsrCachedReader``.
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This reader decorates the original reader and stores all annotations in a PSR-6
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cache:
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.. code-block:: php
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use Doctrine\Common\Annotations\AnnotationReader;
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use Doctrine\Common\Annotations\PsrCachedReader;
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$cache = ... // instantiate a PSR-6 Cache pool
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$reader = new PsrCachedReader(
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new AnnotationReader(),
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$cache,
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$debug = true
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);
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The ``debug`` flag is used here as well to invalidate the cache files
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when the PHP class with annotations changed and should be used during
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development.
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.. warning ::
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The ``AnnotationReader`` works and caches under the
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assumption that all annotations of a doc-block are processed at
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once. That means that annotation classes that do not exist and
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aren't loaded and cannot be autoloaded (using the
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AnnotationRegistry) would never be visible and not accessible if a
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cache is used unless the cache is cleared and the annotations
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requested again, this time with all annotations defined.
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By default the annotation reader returns a list of annotations with
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numeric indexes. If you want your annotations to be indexed by their
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class name you can wrap the reader in an ``IndexedReader``:
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.. code-block:: php
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use Doctrine\Common\Annotations\AnnotationReader;
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use Doctrine\Common\Annotations\IndexedReader;
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$reader = new IndexedReader(new AnnotationReader());
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.. warning::
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You should never wrap the indexed reader inside a cached reader,
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only the other way around. This way you can re-use the cache with
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indexed or numeric keys, otherwise your code may experience failures
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due to caching in a numerical or indexed format.
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Registering Annotations
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~~~~~~~~~~~~~~~~~~~~~~~
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As explained in the introduction, Doctrine Annotations uses its own
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autoloading mechanism to determine if a given annotation has a
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corresponding PHP class that can be autoloaded. For annotation
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autoloading you have to configure the
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``Doctrine\Common\Annotations\AnnotationRegistry``. There are three
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different mechanisms to configure annotation autoloading:
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- Calling ``AnnotationRegistry#registerFile($file)`` to register a file
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that contains one or more annotation classes.
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- Calling ``AnnotationRegistry#registerNamespace($namespace, $dirs =
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null)`` to register that the given namespace contains annotations and
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that their base directory is located at the given $dirs or in the
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include path if ``NULL`` is passed. The given directories should *NOT*
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be the directory where classes of the namespace are in, but the base
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directory of the root namespace. The AnnotationRegistry uses a
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namespace to directory separator approach to resolve the correct path.
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- Calling ``AnnotationRegistry#registerLoader($callable)`` to register
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an autoloader callback. The callback accepts the class as first and
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only parameter and has to return ``true`` if the corresponding file
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was found and included.
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.. note::
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Loaders have to fail silently, if a class is not found even if it
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matches for example the namespace prefix of that loader. Never is a
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loader to throw a warning or exception if the loading failed
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otherwise parsing doc block annotations will become a huge pain.
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A sample loader callback could look like:
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.. code-block:: php
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use Doctrine\Common\Annotations\AnnotationRegistry;
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use Symfony\Component\ClassLoader\UniversalClassLoader;
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AnnotationRegistry::registerLoader(function($class) {
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$file = str_replace("\\", DIRECTORY_SEPARATOR, $class) . ".php";
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if (file_exists("/my/base/path/" . $file)) {
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// file_exists() makes sure that the loader fails silently
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require "/my/base/path/" . $file;
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}
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});
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$loader = new UniversalClassLoader();
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AnnotationRegistry::registerLoader(array($loader, "loadClass"));
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Ignoring missing exceptions
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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By default an exception is thrown from the ``AnnotationReader`` if an
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annotation was found that:
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- is not part of the list of ignored "documentation annotations";
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- was not imported through a use statement;
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- is not a fully qualified class that exists.
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You can disable this behavior for specific names if your docblocks do
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not follow strict requirements:
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.. code-block:: php
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$reader = new \Doctrine\Common\Annotations\AnnotationReader();
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AnnotationReader::addGlobalIgnoredName('foo');
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PHP Imports
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~~~~~~~~~~~
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By default the annotation reader parses the use-statement of a php file
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to gain access to the import rules and register them for the annotation
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processing. Only if you are using PHP Imports can you validate the
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correct usage of annotations and throw exceptions if you misspelled an
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annotation. This mechanism is enabled by default.
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To ease the upgrade path, we still allow you to disable this mechanism.
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Note however that we will remove this in future versions:
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.. code-block:: php
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$reader = new \Doctrine\Common\Annotations\AnnotationReader();
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$reader->setEnabledPhpImports(false);
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