155 lines
5.7 KiB
Plaintext
155 lines
5.7 KiB
Plaintext
The heart of an object relational mapper is the mapping information that glues
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everything together. It instructs the EntityManager how it should behave when
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dealing with the different entities.
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++ Core Metadata Drivers
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Doctrine provides a few different ways for you to specify your metadata:
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* **XML files** (XmlDriver)
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* **Class DocBlock Annotations** (AnnotationDriver)
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* **YAML files** (YamlDriver)
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* **PHP Code in files or static functions** (PhpDriver)
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Something important to note about the above drivers is they are all an intermediate
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step to the same end result. The mapping information is populated to
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`Doctrine\ORM\Mapping\ClassMetadata` instances. So in the end, Doctrine
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only ever has to work with the api of the `ClassMetadata` class to get mapping
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information for an entity.
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> **TIP**
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> The populated `ClassMetadata` instances are also cached so in a production
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> environment the parsing and populating only ever happens once. You can configure
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> the metadata cache implementation using the `setMetadataCacheImpl()` method on
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> the `Doctrine\ORM\Configuration` class:
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>
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> [php]
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> $em->getConfiguration()->setMetadataCacheImpl(new ApcCache());
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If you want to use one of the included core metadata drivers you just need to
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configure it. All the drivers are in the `Doctrine\ORM\Mapping\Driver` namespace:
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[php]
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$driver = new \Doctrine\ORM\Mapping\Driver\XmlDriver('/path/to/mapping/files');
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$em->getConfiguration()->setMetadataDriverImpl($driver);
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++ Implementing Metadata Drivers
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In addition to the included metadata drivers you can very easily implement
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your own. All you need to do is define a class which implements the `Driver`
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interface:
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[php]
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namespace Doctrine\ORM\Mapping\Driver;
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use Doctrine\ORM\Mapping\ClassMetadataInfo;
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interface Driver
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{
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/**
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* Loads the metadata for the specified class into the provided container.
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*
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* @param string $className
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* @param ClassMetadataInfo $metadata
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*/
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function loadMetadataForClass($className, ClassMetadataInfo $metadata);
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/**
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* Gets the names of all mapped classes known to this driver.
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*
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* @return array The names of all mapped classes known to this driver.
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*/
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function getAllClassNames();
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/**
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* Whether the class with the specified name should have its metadata loaded.
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* This is only the case if it is either mapped as an Entity or a
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* MappedSuperclass.
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*
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* @param string $className
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* @return boolean
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*/
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function isTransient($className);
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}
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If you want to write a metadata driver to parse information from some file format
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we've made your life a little easier by providing the `AbstractFileDriver`
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implementation for you to extend from:
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[php]
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class MyMetadataDriver extends AbstractFileDriver
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{
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/**
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* {@inheritdoc}
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*/
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protected $_fileExtension = '.dcm.ext';
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/**
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* {@inheritdoc}
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*/
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public function loadMetadataForClass($className, ClassMetadataInfo $metadata)
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{
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$data = $this->_loadMappingFile($file);
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// populate ClassMetadataInfo instance from $data
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}
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/**
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* {@inheritdoc}
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*/
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protected function _loadMappingFile($file)
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{
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// parse contents of $file and return php data structure
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}
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}
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> **NOTE**
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> When using the `AbstractFileDriver` it requires that you only have one entity
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> defined per file and the file named after the class described inside where
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> namespace separators are replaced by periods. So if you have an entity named
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> `Entities\User` and you wanted to write a mapping file for your driver above
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> you would need to name the file `Entities.User.dcm.ext` for it to be recognized.
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Now you can use your `MyMetadataDriver` implementation by setting it with the
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`setMetadataDriverImpl()` method:
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[php]
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$driver = new MyMetadataDriver('/path/to/mapping/files');
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$em->getConfiguration()->setMetadataDriverImpl($driver);
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++ ClassMetadata
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The last piece you need to know and understand about metadata in Doctrine 2 is
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the API of the `ClassMetadata` classes. You need to be familiar with them in order
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to implement your own drivers but more importantly to retrieve mapping information
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for a certain entity when needed.
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You have all the methods you need to manually specify the mapping information
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instead of using some mapping file to populate it from. The base `ClassMetadataInfo`
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class is responsible for only data storage and is not meant for runtime use. It
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does not require that the class actually exists yet so it is useful for describing some
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entity before it exists and using that information to generate for example the
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entities themselves. The class `ClassMetadata` extends `ClassMetadataInfo` and
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adds some functionality required for runtime usage and requires that the PHP
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class is present and can be autoloaded.
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You can read more about the API of the `ClassMetadata` classes in the PHP Mapping
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chapter.
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++ Getting ClassMetadata Instances
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If you want to get the `ClassMetadata` instance for an entity in your project
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to programatically use some mapping information to generate some HTML or something
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similar you can retrieve it through the `ClassMetadataFactory`:
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[php]
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$cmf = $em->getMetadataFactory();
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$class = $cmf->getMetadataFor('MyEntityName');
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Now you can learn about the entity and use the data stored in the `ClassMetadata`
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instance to get all mapped fields for example and iterate over them:
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[php]
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foreach ($class->fieldMappings as $fieldMapping) {
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echo $fieldMapping['fieldName'] . "\n";
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} |