Parser for metadata

1.2.0 2023-11-07 14:24 UTC

This package is auto-updated.

Last update: 2024-05-08 18:05:34 UTC


This project is Open Sourced based on work that we did initially as closed source at Liip, it may be lacking some documentation. If there is anything that you need or have questions about we would love to see you open an issue! :)

This is a parser for building model metadata from PHP classes. The metadata model can then be used to generate code or configuration. For example a serializer or ElasticSearch schema for types.

The metadata is geared toward this use case. PHP level constructs that represent the same information are grouped together: Methods for virtual properties and fields that have the same serialized name, but are valid in different versions.

This extensible parser can process PHP code and annotations or other metadata. You could write your own parsers, but this library comes with support for:

  • Reflection
  • PhpDoc
  • JMSSerializer annotations


If you want to contribute to the project (awesome!!), please read the Contributing Guidelines and adhere to our Code Of Conduct

Where do I go for help?

If you need, open an issue.


use Doctrine\Common\Annotations\AnnotationReader;
use Liip\MetadataParser\Builder;
use Liip\MetadataParser\Parser;
use Liip\MetadataParser\RecursionChecker;
use Liip\MetadataParser\ModelParser\JMSParser;
use Liip\MetadataParser\ModelParser\LiipMetadataAnnotationParser;
use Liip\MetadataParser\ModelParser\PhpDocParser;
use Liip\MetadataParser\ModelParser\ReflectionParser;
use Liip\MetadataParser\ModelParser\VisibilityAwarePropertyAccessGuesser;

$parser = new Parser(
    new ReflectionParser(),
    new PhpDocParser(),
    new JMSParser(new AnnotationReader()),
    new VisibilityAwarePropertyAccessGuesser(),
    new LiipMetadataAnnotationParser(new AnnotationReader()),

$recursionChecker = new RecursionChecker(new NullLogger());

$builder = new Builder($parser, $recursionChecker);


The Builder::build method is the main entry point to get a ClassMetadata object. The builder accepts an array of Reducer to select which property to use when there are several options. A reducer can lead to drop a property if none of the variants is acceptable. Multiple options for a single field mainly come from the @SerializedName and @VirtualProperty annotations of JMSSerializer:

  • GroupReducer: Select the property based on whether it is in any of the specified groups;
  • VersionReducer: Select the property based on whether it is included in the specified version;
  • TakeBestReducer: Make sure that we end up with the property that has the same name as the serialized name, if we still have multiple options after the other reducers.
use Liip\MetadataParser\Reducer\GroupReducer;
use Liip\MetadataParser\Reducer\PreferredReducer;
use Liip\MetadataParser\Reducer\TakeBestReducer;
use Liip\MetadataParser\Reducer\VersionReducer;

$reducers = [
    new VersionReducer('2'),
    new GroupReducer(['api', 'detail']),
    new PreferredReducer(),
    new TakeBestReducer(),
$metadata = $builder->build(MyClass::class, $reducers);

The ClassMetadata provides all information on a class. Properties have a PropertyType to tell what kind of property they are. Properties that hold another class, are of the type PropertyTypeClass that has the method getClassMetadata() to get the metadata of the nested class. This structure is validated to not contain any infinite recursion.

Property naming strategy

By default, property names will be translated from a camelCased to a lower and snake_cased name (e.g. myProperty becomes my_property). If you want to keep the property name as is, you can change the strategy to identical via the following code:


Handling Edge Cases with @Preferred

This library provides its own annotation in Liip\MetadataParser\Annotation\Preferred to specify which property to use in case there are several options. This can be useful for example when serializing models without specifying a version, when they use different virtual properties in different versions.

use JMS\Serializer\Annotation as JMS;
use Liip\MetadataParser\Annotation as Liip;

class Product
     * @JMS\Since("2")
     * @JMS\Type("string")
    public $name;
     * @JMS\Until("1")
     * @JMS\SerializedName("name")
     * @JMS\Type("string")
     * @Liip\Preferred
    public $legacyName;

Expected Recursion: Working with Flawed Models

JMS annotation

If you are using JMS annotations, you can add the MaxDepth annotation to properties that might be recursive.

The following example will tell the metadata parser that the recursion is expected up to a maximum depth of 3.

use JMS\Serializer\Annotation as JMS;

class RecursionModel 
     * @JMS\MaxDepth(3)
     * @JMS\Type("RecursionModel")
    public $recursion;

Pure PHP

The RecursionChecker accepts a second parameter to specify places where to break recursion. This is useful if your model tree looks like it has recursions but actually does not have them. JMSSerializer always acts on the actual data and therefore does not notice a recursion as long as it is not infinite.

For example, lets say you have a Product that has a field variants which is again list of Product. Those variant products use the same class and therefore have the variants field. However, in real data a variant never contains further variants. To avoid a recursion exception for this example, you would specify:

$expectedRecursions = [
    ['variants', 'variants'],
$recursionChecker = new RecursionChecker(new NullLogger(), $expectedRecursions);

With this configuration, the ClassMetadata found in the property type for the variants property of the final model will have no field variants, so that code working on the metadata does not need to worry about infinite recursion.

Extending the metadata parser

This library comes with a couple of parsers, but you can write your own to handle custom information specific to your project. Use the PropertyVariationMetadata::setCustomInformation method to add custom data, and use PropertyMetadata::getCustomInformation to read it in your metadata consumers.