How to Use the Serializer
=========================

Symfony provides a serializer to transform data structures from one format
to PHP objects and the other way around.

This is most commonly used when building an API or communicating with third
party APIs. The serializer can transform an incoming JSON request payload
to a PHP object that is consumed by your application. Then, when generating
the response, you can use the serializer to transform the PHP objects back
to a JSON response.

It can also be used to for instance load CSV configuration data as PHP
objects, or even to transform between formats (e.g. YAML to XML).

.. _activating_the_serializer:

Installation
------------

In applications using :ref:`Symfony Flex <symfony-flex>`, run this command to
install the serializer :ref:`Symfony pack <symfony-packs>` before using it:

.. code-block:: terminal

    $ composer require symfony/serializer-pack

.. note::

    The serializer pack also installs some commonly used optional
    dependencies of the Serializer component. When using this component
    outside the Symfony framework, you might want to start with the
    ``symfony/serializer`` package and install optional dependencies if you
    need them.

.. seealso::

    A popular alternative to the Symfony Serializer component is the third-party
    library, `JMS serializer`_.

Serializing an Object
---------------------

For this example, assume the following class exists in your project::

    // src/Model/Person.php
    namespace App\Model;

    class Person
    {
        public function __construct(
            private int $age,
            private string $name,
            private bool $sportsperson
        ) {
        }

        public function getAge(): int
        {
            return $this->age;
        }

        public function getName(): string
        {
            return $this->name;
        }

        public function isSportsperson(): bool
        {
            return $this->sportsperson;
        }
    }

If you want to transform objects of this type into a JSON structure (e.g.
to send them via an API response), get the ``serializer`` service by using
the :class:`Symfony\\Component\\Serializer\\SerializerInterface` parameter type:

.. configuration-block::

    .. code-block:: php-symfony

        // src/Controller/PersonController.php
        namespace App\Controller;

        use App\Model\Person;
        use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
        use Symfony\Component\HttpFoundation\JsonResponse;
        use Symfony\Component\HttpFoundation\Response;
        use Symfony\Component\Serializer\SerializerInterface;

        class PersonController extends AbstractController
        {
            public function index(SerializerInterface $serializer): Response
            {
                $person = new Person('Jane Doe', 39, false);

                $jsonContent = $serializer->serialize($person, 'json');
                // $jsonContent contains {"name":"Jane Doe","age":39,"sportsperson":false}

                return JsonResponse::fromJsonString($jsonContent);
            }
        }

    .. code-block:: php-standalone

        use App\Model\Person;
        use Symfony\Component\Serializer\Encoder\JsonEncoder;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        $encoders = [new JsonEncoder()];
        $normalizers = [new ObjectNormalizer()];
        $serializer = new Serializer($normalizers, $encoders);

        $person = new Person('Jane Done', 39, false);

        $jsonContent = $serializer->serialize($person, 'json');
        // $jsonContent contains {"name":"Jane Doe","age":39,"sportsperson":false}

The first parameter of the :method:`Symfony\\Component\\Serializer\\Serializer::serialize`
is the object to be serialized and the second is used to choose the proper
encoder (i.e. format), in this case the :class:`Symfony\\Component\\Serializer\\Encoder\\JsonEncoder`.

.. tip::

    When your controller class extends ``AbstractController`` (like in the
    example above), you can simplify your controller by using the
    :method:`Symfony\\Bundle\\FrameworkBundle\\Controller\\AbstractController::json`
    method to create a JSON response from an object using the Serializer::

        class PersonController extends AbstractController
        {
            public function index(): Response
            {
                $person = new Person('Jane Doe', 39, false);

                // when the Serializer is not available, this will use json_encode()
                return $this->json($person);
            }
        }

Using the Serializer in Twig Templates
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also serialize objects in any Twig template using the ``serialize``
filter:

.. code-block:: twig

    {{ person|serialize(format = 'json') }}

See the :ref:`twig reference <reference-twig-filter-serialize>` for more
information.

Deserializing an Object
-----------------------

APIs often also need to convert a formatted request body (e.g. JSON) to a
PHP object. This process is called *deserialization* (also known as "hydration"):

.. configuration-block::

    .. code-block:: php-symfony

        // src/Controller/PersonController.php
        namespace App\Controller;

        // ...
        use Symfony\Component\HttpFoundation\Exception\BadRequestException;
        use Symfony\Component\HttpFoundation\Request;

        class PersonController extends AbstractController
        {
            // ...

            public function create(Request $request, SerializerInterface $serializer): Response
            {
                if ('json' !== $request->getContentTypeFormat()) {
                    throw new BadRequestException('Unsupported content format');
                }

                $jsonData = $request->getContent();
                $person = $serializer->deserialize($jsonData, Person::class, 'json');

                // ... do something with $person and return a response
            }
        }

    .. code-block:: php-standalone

        use App\Model\Person;
        use Symfony\Component\Serializer\Encoder\JsonEncoder;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        // ...
        $jsonData = ...; // fetch JSON from the request
        $person = $serializer->deserialize($jsonData, Person::class, 'json');

In this case, :method:`Symfony\\Component\\Serializer\\Serializer::deserialize`
needs three parameters:

#. The data to be decoded
#. The name of the class this information will be decoded to
#. The name of the encoder used to convert the data to an array (i.e. the
   input format)

When sending a request to this controller (e.g.
``{"first_name":"John Doe","age":54,"sportsperson":true}``), the serializer
will create a new instance of ``Person`` and sets the properties to the
values from the given JSON.

.. note::

    By default, additional attributes that are not mapped to the
    denormalized object will be ignored by the Serializer component. For
    instance, if a request to the above controller contains ``{..., "city": "Paris"}``,
    the ``city`` field will be ignored. You can also throw an exception in
    these cases using the :ref:`serializer context <serializer-context>`
    you'll learn about later.

.. seealso::

    You can also deserialize data into an existing object instance (e.g.
    when updating data). See :ref:`Deserializing in an Existing Object <serializer-populate-existing-object>`.

.. _serializer-process:

The Serialization Process: Normalizers and Encoders
---------------------------------------------------

The serializer uses a two-step process when (de)serializing objects:

.. raw:: html

    <object data="_images/serializer/serializer_workflow.svg" type="image/svg+xml"
        alt="A flow diagram showing how objects are serialized/deserialized. This is described in the subsequent paragraph."
    ></object>

In both directions, data is always first converted to an array. This splits
the process in two separate responsibilities:

Normalizers
    These classes convert **objects** into **arrays** and vice versa. They
    do the heavy lifting of finding out which class properties to
    serialize, what value they hold and what name they should have.
Encoders
    Encoders convert **arrays** into a specific **format** and the other
    way around. Each encoder knows exactly how to parse and generate a
    specific format, for instance JSON or XML.

Internally, the ``Serializer`` class uses a sorted list of normalizers and
one encoder for the specific format when (de)serializing an object.

There are several normalizers configured in the default ``serializer``
service. The most important normalizer is the
:class:`Symfony\\Component\\Serializer\\Normalizer\\ObjectNormalizer`. This
normalizer uses reflection and the :doc:`PropertyAccess component </components/property_access>`
to transform between any object and an array. You'll learn more about
:ref:`this and other normalizers <serializer-normalizers>` later.

The default serializer is also configured with some encoders, covering the
common formats used by HTTP applications:

* :class:`Symfony\\Component\\Serializer\\Encoder\\JsonEncoder`
* :class:`Symfony\\Component\\Serializer\\Encoder\\XmlEncoder`
* :class:`Symfony\\Component\\Serializer\\Encoder\\CsvEncoder`
* :class:`Symfony\\Component\\Serializer\\Encoder\\YamlEncoder`

Read more about these encoders and their configuration in
:doc:`/serializer/encoders`.

.. tip::

    The `API Platform`_ project provides encoders for more advanced
    formats:

    * `JSON-LD`_ along with the `Hydra Core Vocabulary`_
    * `OpenAPI`_ v2 (formerly Swagger) and v3
    * `GraphQL`_
    * `JSON:API`_
    * `HAL`_

.. _serializer-context:

Serializer Context
~~~~~~~~~~~~~~~~~~

The serializer, and its normalizers and encoders, are configured through
the *serializer context*. This context can be configured in multiple
places:

* :ref:`Globally through the framework configuration <serializer-default-context>`
* :ref:`While serializing/deserializing <serializer-context-while-serializing-deserializing>`
* :ref:`For a specific property <serializer-using-context-builders>`

You can use all three options at the same time. When the same setting is
configured in multiple places, the latter in the list above will override
the previous one (e.g. the setting on a specific property overrides the one
configured globally).

.. _serializer-default-context:

Configure a Default Context
...........................

You can configure a default context in the framework configuration, for
instance to disallow extra fields while deserializing:

.. configuration-block::

    .. code-block:: yaml

        # config/packages/serializer.yaml
        framework:
            serializer:
                default_context:
                    allow_extra_attributes: false

    .. code-block:: xml

        <!-- config/packages/serializer.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xmlns:framework="http://symfony.com/schema/dic/symfony"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                https://symfony.com/schema/dic/services/services-1.0.xsd
                http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

            <framework:config>
                <framework:serializer>
                    <framework:default-context>
                        <framework:allow-extra-attributes>false</framework:allow-extra-attributes>
                    </framework:default-context>
                </framework:serializer>
            </framework:config>
        </container>

    .. code-block:: php

        // config/packages/serializer.php
        use Symfony\Config\FrameworkConfig;

        return static function (FrameworkConfig $framework): void {
            $framework->serializer()
                ->defaultContext('', [
                    'allow_extra_attributes' => false,
                ])
            ;
        };

    .. code-block:: php-standalone

        use Symfony\Component\Serializer\NameConverter\CamelCaseToSnakeCaseNameConverter;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

        // ...
        $normalizers = [
            new ObjectNormalizer(null, null, null, null, null, null, [
                'allow_extra_attributes' => false,
            ]),
        ];
        $serializer = new Serializer($normalizers, $encoders);

.. _serializer-context-while-serializing-deserializing:

Pass Context while Serializing/Deserializing
............................................

You can also configure the context for a single call to
``serialize()``/``deserialize()``. For instance, you can skip
properties with a ``null`` value only for one serialize call::

    use Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer;

    // ...
    $serializer->serialize($person, 'json', [
        AbstractObjectNormalizer::SKIP_NULL_VALUES => true
    ]);

    // next calls to serialize() will NOT skip null values

.. _serializer-using-context-builders:

Using Context Builders
""""""""""""""""""""""

You can use "context builders" to help define the (de)serialization
context. Context builders are PHP objects that provide autocompletion,
validation, and documentation of context options::

    use Symfony\Component\Serializer\Context\Normalizer\DateTimeNormalizerContextBuilder;

    $contextBuilder = (new DateTimeNormalizerContextBuilder())
        ->withFormat('Y-m-d H:i:s');
    $serializer->serialize($something, 'json', $contextBuilder->toArray());

Each normalizer/encoder has its related context builder. To create a more
complex (de)serialization context, you can chain them using the
``withContext()`` method::

    use Symfony\Component\Serializer\Context\Encoder\CsvEncoderContextBuilder;
    use Symfony\Component\Serializer\Context\Normalizer\ObjectNormalizerContextBuilder;

    $initialContext = [
        'custom_key' => 'custom_value',
    ];

    $contextBuilder = (new ObjectNormalizerContextBuilder())
        ->withContext($initialContext)
        ->withGroups(['group1', 'group2']);

    $contextBuilder = (new CsvEncoderContextBuilder())
        ->withContext($contextBuilder)
        ->withDelimiter(';');

    $serializer->serialize($something, 'csv', $contextBuilder->toArray());

.. seealso::

    You can also :doc:`create your context builders </serializer/custom_context_builders>`
    to have autocompletion, validation, and documentation for your custom
    context values.

Configure Context on a Specific Property
........................................

At last, you can also configure context values on a specific object
property. For instance, to configure the datetime format:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php

        // ...
        use Symfony\Component\Serializer\Attribute\Context;
        use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;

        class Person
        {
            #[Context([DateTimeNormalizer::FORMAT_KEY => 'Y-m-d'])]
            public \DateTimeImmutable $createdAt;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Model\Person:
            attributes:
                createdAt:
                    contexts:
                        - context: { datetime_format: 'Y-m-d' }

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="createdAt">
                    <context>
                        <entry name="datetime_format">Y-m-d</entry>
                    </context>
                </attribute>
            </class>
        </serializer>

.. note::

    When using YAML or XML, the mapping files must be placed in one of
    these locations:

    * All ``*.yaml`` and ``*.xml`` files in the ``config/serializer/``
      directory.
    * The ``serialization.yaml`` or ``serialization.xml`` file in the
      ``Resources/config/`` directory of a bundle;
    * All ``*.yaml`` and ``*.xml`` files in the ``Resources/config/serialization/``
      directory of a bundle.

You can also specify a context specific to normalization or denormalization:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php

        // ...
        use Symfony\Component\Serializer\Attribute\Context;
        use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;

        class Person
        {
            #[Context(
                normalizationContext: [DateTimeNormalizer::FORMAT_KEY => 'Y-m-d'],
                denormalizationContext: [DateTimeNormalizer::FORMAT_KEY => \DateTime::RFC3339],
            )]
            public \DateTimeImmutable $createdAt;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Model\Person:
            attributes:
                createdAt:
                    contexts:
                        - normalizationContext: { datetime_format: 'Y-m-d' }
                          denormalizationContext: { datetime_format: !php/const \DateTime::RFC3339 }

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="createdAt">
                    <normalization-context>
                        <entry name="datetime_format">Y-m-d</entry>
                    </normalization-context>

                    <denormalization-context>
                        <entry name="datetime_format">Y-m-d\TH:i:sP</entry>
                    </denormalization-context>
                </attribute>
            </class>
        </serializer>

.. _serializer-context-group:

You can also restrict the usage of a context to some
:ref:`groups <serializer-groups-attribute>`:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php

        // ...
        use Symfony\Component\Serializer\Attribute\Context;
        use Symfony\Component\Serializer\Attribute\Groups;
        use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;

        class Person
        {
            #[Groups(['extended'])]
            #[Context([DateTimeNormalizer::FORMAT_KEY => \DateTime::RFC3339])]
            #[Context(
                context: [DateTimeNormalizer::FORMAT_KEY => \DateTime::RFC3339_EXTENDED],
                groups: ['extended'],
            )]
            public \DateTimeImmutable $createdAt;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Model\Person:
            attributes:
                createdAt:
                    groups: [extended]
                    contexts:
                        - context: { datetime_format: !php/const \DateTime::RFC3339 }
                        - context: { datetime_format: !php/const \DateTime::RFC3339_EXTENDED }
                          groups: [extended]

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="createdAt">
                    <group>extended</group>

                    <context>
                        <entry name="datetime_format">Y-m-d\TH:i:sP</entry>
                    </context>
                    <context>
                        <entry name="datetime_format">Y-m-d\TH:i:s.vP</entry>
                        <group>extended</group>
                    </context>
                </attribute>
            </class>
        </serializer>

The attribute can be repeated as much as needed on a single property.
Context without group is always applied first. Then context for the
matching groups are merged in the provided order.

If you repeat the same context in multiple properties, consider using the
``#[Context]`` attribute on your class to apply that context configuration to
all the properties of the class::

    namespace App\Model;

    use Symfony\Component\Serializer\Attribute\Context;
    use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;

    #[Context([DateTimeNormalizer::FORMAT_KEY => \DateTime::RFC3339])]
    #[Context(
        context: [DateTimeNormalizer::FORMAT_KEY => \DateTime::RFC3339_EXTENDED],
        groups: ['extended'],
    )]
    class Person
    {
        // ...
    }

Serializing to or from PHP Arrays
---------------------------------

The default :class:`Symfony\\Component\\Serializer\\Serializer` can also be
used to only perform one step of the :ref:`two step serialization process <serializer-process>`
by using the respective interface:

.. configuration-block::

    .. code-block:: php-symfony

        use Symfony\Component\Serializer\Encoder\DecoderInterface;
        use Symfony\Component\Serializer\Encoder\EncoderInterface;
        use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
        use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
        // ...

        class PersonController extends AbstractController
        {
            public function index(DenormalizerInterface&NormalizerInterface $serializer): Response
            {
                $person = new Person('Jane Doe', 39, false);

                // use normalize() to convert a PHP object to an array
                $personArray = $serializer->normalize($person, 'json');

                // ...and denormalize() to convert an array back to a PHP object
                $personCopy = $serializer->denormalize($personArray, Person::class);

                // ...
            }

            public function json(DecoderInterface&EncoderInterface $serializer): Response
            {
                $data = ['name' => 'Jane Doe'];

                // use encode() to transform PHP arrays into another format
                $json = $serializer->encode($data, 'json');

                // ...and decode() to transform any format to just PHP arrays (instead of objects)
                $data = $serializer->decode('{"name":"Charlie Doe"}', 'json');
                // $data contains ['name' => 'Charlie Doe']
            }
        }

    .. code-block:: php-standalone

        use App\Model\Person;
        use Symfony\Component\Serializer\Encoder\JsonEncoder;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        $encoders = [new JsonEncoder()];
        $normalizers = [new ObjectNormalizer()];
        $serializer = new Serializer($normalizers, $encoders);

        // use normalize() to convert a PHP object to an array
        $personArray = $serializer->normalize($person, 'json');

        // ...and denormalize() to convert an array back to a PHP object
        $personCopy = $serializer->denormalize($personArray, Person::class);

        $data = ['name' => 'Jane Doe'];

        // use encode() to transform PHP arrays into another format
        $json = $serializer->encode($data, 'json');

        // ...and decode() to transform any format to just PHP arrays (instead of objects)
        $data = $serializer->decode('{"name":"Charlie Doe"}', 'json');
        // $data contains ['name' => 'Charlie Doe']

.. _serializer_ignoring-attributes:

Ignoring Properties
-------------------

The ``ObjectNormalizer`` normalizes *all* properties of an object and all
methods starting with ``get*()``, ``has*()``, ``is*()`` and ``can*()``.
Some properties or methods should never be serialized. You can exclude
them using the ``#[Ignore]`` attribute:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php
        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\Ignore;

        class Person
        {
            // ...

            #[Ignore]
            public function isPotentiallySpamUser(): bool
            {
                // ...
            }
        }

    .. code-block:: yaml

        App\Model\Person:
            attributes:
                potentiallySpamUser:
                    ignore: true

    .. code-block:: xml

        <?xml version="1.0" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="potentiallySpamUser" ignore="true"/>
            </class>
        </serializer>

The ``potentiallySpamUser`` property will now never be serialized:

.. configuration-block::

    .. code-block:: php-symfony

        use App\Model\Person;

        // ...
        $person = new Person('Jane Doe', 32, false);
        $json = $serializer->serialize($person, 'json');
        // $json contains {"name":"Jane Doe","age":32,"sportsperson":false}

        $person1 = $serializer->deserialize(
            '{"name":"Jane Doe","age":32,"sportsperson":false","potentiallySpamUser":false}',
            Person::class,
            'json'
        );
        // the "potentiallySpamUser" value is ignored

    .. code-block:: php-standalone

        use App\Model\Person;
        use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
        use Symfony\Component\Serializer\Mapping\Loader\AttributeLoader;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        // ...

        // you need to pass a class metadata factory with a loader to the
        // ObjectNormalizer when reading mapping information like Ignore or Groups.
        // E.g. when using PHP attributes:
        $classMetadataFactory = new ClassMetadataFactory(new AttributeLoader());
        $normalizers = [new ObjectNormalizer($classMetadataFactory)];

        $serializer = new Serializer($normalizers, $encoders);

        $person = new Person('Jane Doe', 32, false);
        $json = $serializer->serialize($person, 'json');
        // $json contains {"name":"Jane Doe","age":32,"sportsperson":false}

        $person1 = $serializer->deserialize(
            '{"name":"Jane Doe","age":32,"sportsperson":false","potentiallySpamUser":false}',
            Person::class,
            'json'
        );
        // the "potentiallySpamUser" value is ignored

Ignoring Attributes Using the Context
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also pass an array of attribute names to ignore at runtime using
the ``ignored_attributes`` context options::

    use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;

    // ...
    $person = new Person('Jane Doe', 32, false);
    $json = $serializer->serialize($person, 'json',
    [
        AbstractNormalizer::IGNORED_ATTRIBUTES => ['age'],
    ]);
    // $json contains {"name":"Jane Doe","sportsperson":false}

However, this can quickly become unmaintainable if used excessively. See
the next section about *serialization groups* for a better solution.

.. _serializer-groups-attribute:

Selecting Specific Properties
-----------------------------

Instead of excluding a property or method in all situations, you might need
to exclude some properties in one place, but serialize them in another.
Groups are a handy way to achieve this.

You can add the ``#[Groups]`` attribute to your class:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php
        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\Groups;

        class Person
        {
            #[Groups(["admin-view"])]
            private int $age;

            #[Groups(["public-view"])]
            private string $name;

            #[Groups(["public-view"])]
            private bool $sportsperson;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Model\Person:
            attributes:
                age:
                    groups: ['admin-view']
                name:
                    groups: ['public-view']
                sportsperson:
                    groups: ['public-view']

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="age">
                    <group>admin-view</group>
                </attribute>
                <attribute name="name">
                    <group>public-view</group>
                </attribute>
                <attribute name="sportsperson">
                    <group>public-view</group>
                </attribute>
            </class>
        </serializer>

You can now choose which groups to use when serializing::

    $json = $serializer->serialize(
        $person,
        'json',
        ['groups' => 'public-view']
    );
    // $json contains {"name":"Jane Doe","sportsperson":false}

    // you can also pass an array of groups
    $json = $serializer->serialize(
        $person,
        'json',
        ['groups' => ['public-view', 'admin-view']]
    );
    // $json contains {"name":"Jane Doe","age":32,"sportsperson":false}

    // or use the special "*" value to select all groups
    $json = $serializer->serialize(
        $person,
        'json',
        ['groups' => '*']
    );
    // $json contains {"name":"Jane Doe","age":32,"sportsperson":false}

Using the Serialization Context
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

At last, you can also use the ``attributes`` context option to select
properties at runtime::

    use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;
    // ...

    $json = $serializer->serialize($person, 'json', [
        AbstractNormalizer::ATTRIBUTES => ['name', 'company' => ['name']]
    ]);
    // $json contains {"name":"Dunglas","company":{"name":"Les-Tilleuls.coop"}}

Only attributes that are :ref:`not ignored <serializer_ignoring-attributes>`
are available. If serialization groups are set, only attributes allowed by
those groups can be used.

.. _serializer-handling-arrays:

Handling Arrays
---------------

The serializer is capable of handling arrays of objects. Serializing arrays
works just like serializing a single object::

    use App\Model\Person;

    // ...
    $person1 = new Person('Jane Doe', 39, false);
    $person2 = new Person('John Smith', 52, true);

    $persons = [$person1, $person2];
    $JsonContent = $serializer->serialize($persons, 'json');

    // $jsonContent contains [{"name":"Jane Doe","age":39,"sportsman":false},{"name":"John Smith","age":52,"sportsman":true}]

To deserialize a list of objects, you have to append ``[]`` to the type
parameter::

    // ...

    $jsonData = ...; // the serialized JSON data from the previous example
    $persons = $serializer->deserialize($JsonData, Person::class.'[]', 'json');

For nested classes, you have to add a PHPDoc type to the property, constructor or setter::

    // src/Model/UserGroup.php
    namespace App\Model;

    class UserGroup
    {
        /**
         * @param Person[] $members
         */
        public function __construct(
            private array $members,
        ) {
        }

        // or if you're using a setter

        /**
         * @param Person[] $members
         */
        public function setMembers(array $members): void
        {
            $this->members = $members;
        }

        // ...
    }

.. tip::

    The Serializer also supports array types used in static analysis, like
    ``list<Person>`` and ``array<Person>``. Make sure the
    ``phpstan/phpdoc-parser`` and ``phpdocumentor/reflection-docblock``
    packages are installed (these are part of the ``symfony/serializer-pack``).

.. _serializer-nested-structures:

Deserializing Nested Structures
-------------------------------

Some APIs might provide verbose nested structures that you want to flatten
in the PHP object. For instance, imagine a JSON response like this:

.. code-block:: json

    {
        "id": "123",
        "profile": {
            "username": "jdoe",
            "personal_information": {
                "full_name": "Jane Doe"
            }
        }
    }

You may wish to serialize this information to a single PHP object like::

    class Person
    {
        private int $id;
        private string $username;
        private string $fullName;
    }

Use the ``#[SerializedPath]`` to specify the path of the nested property
using :doc:`valid PropertyAccess syntax </components/property_access>`:

.. configuration-block::

    .. code-block:: php-attributes

        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\SerializedPath;

        class Person
        {
            private int $id;

            #[SerializedPath('[profile][username]')]
            private string $username;

            #[SerializedPath('[profile][personal_information][full_name]')]
            private string $fullName;
        }

    .. code-block:: yaml

        App\Model\Person:
            attributes:
                username:
                    serialized_path: '[profile][username]'
                fullName:
                    serialized_path: '[profile][personal_information][full_name]'

    .. code-block:: xml

        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="username" serialized-path="[profile][username]"/>
                <attribute name="fullName" serialized-path="[profile][personal_information][full_name]"/>
            </class>
        </serializer>

.. warning::

    The ``SerializedPath`` cannot be used in combination with a
    ``SerializedName`` for the same property.

The ``#[SerializedPath]`` attribute also applies to the serialization of a
PHP object::

    use App\Model\Person;
    // ...

    $person = new Person(123, 'jdoe', 'Jane Doe');
    $jsonContent = $serializer->serialize($person, 'json');
    // $jsonContent contains {"id":123,"profile":{"username":"jdoe","personal_information":{"full_name":"Jane Doe"}}}

.. _serializer-name-conversion:

Converting Property Names when Serializing and Deserializing
------------------------------------------------------------

Sometimes serialized attributes must be named differently than properties
or getter/setter methods of PHP classes. This can be achieved using name
converters.

The serializer service uses the
:class:`Symfony\\Component\\Serializer\\NameConverter\\MetadataAwareNameConverter`.
With this name converter, you can change the name of an attribute using
the ``#[SerializedName]`` attribute:

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php
        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\SerializedName;

        class Person
        {
            #[SerializedName('customer_name')]
            private string $name;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Entity\Person:
            attributes:
                name:
                    serialized_name: customer_name

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Entity\Person">
                <attribute name="name" serialized-name="customer_name"/>
            </class>
        </serializer>

This custom mapping is used to convert property names when serializing and
deserializing objects:

.. configuration-block::

    .. code-block:: php-symfony

        // ...

        $json = $serializer->serialize($person, 'json');
        // $json contains {"customer_name":"Jane Doe", ...}

    .. code-block:: php-standalone

        use App\Model\Person;
        use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
        use Symfony\Component\Serializer\Mapping\Loader\AttributeLoader;
        use Symfony\Component\Serializer\NameConverter\MetadataAwareNameConverter;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        // ...

        // Configure a loader to retrieve mapping information like SerializedName.
        // E.g. when using PHP attributes:
        $classMetadataFactory = new ClassMetadataFactory(new AttributeLoader());
        $nameConverter = new MetadataAwareNameConverter($classMetadataFactory);
        $normalizers = [
            new ObjectNormalizer($classMetadataFactory, $nameConverter),
        ];

        $serializer = new Serializer($normalizers, $encoders);

        $person = new Person('Jane Doe', 32, false);
        $json = $serializer->serialize($person, 'json');
        // $json contains {"customer_name":"Jane Doe", ...}

.. seealso::

    You can also create a custom name converter class. Read more about this
    in :doc:`/serializer/custom_name_converter`.

.. _using-camelized-method-names-for-underscored-attributes:

CamelCase to snake_case
~~~~~~~~~~~~~~~~~~~~~~~

In many formats, it's common to use underscores to separate words (also known
as snake_case). However, in Symfony applications is common to use camelCase to
name properties.

Symfony provides a built-in name converter designed to transform between
snake_case and CamelCased styles during serialization and deserialization
processes. You can use it instead of the metadata aware name converter by
setting the ``name_converter`` setting to
``serializer.name_converter.camel_case_to_snake_case``:

.. configuration-block::

    .. code-block:: yaml

        # config/packages/serializer.yaml
        framework:
            serializer:
                name_converter: 'serializer.name_converter.camel_case_to_snake_case'

    .. code-block:: xml

        <!-- config/packages/serializer.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xmlns:framework="http://symfony.com/schema/dic/symfony"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                https://symfony.com/schema/dic/services/services-1.0.xsd
                http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

            <framework:config>
                <framework:serializer
                    name-converter="serializer.name_converter.camel_case_to_snake_case"
                />
            </framework:config>
        </container>

    .. code-block:: php

        // config/packages/serializer.php
        use Symfony\Config\FrameworkConfig;

        return static function (FrameworkConfig $framework): void {
            $framework->serializer()
                ->nameConverter('serializer.name_converter.camel_case_to_snake_case')
            ;
        };

    .. code-block:: php-standalone

        use Symfony\Component\Serializer\NameConverter\CamelCaseToSnakeCaseNameConverter;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

        // ...
        $normalizers = [
            new ObjectNormalizer(null, new CamelCaseToSnakeCaseNameConverter()),
        ];
        $serializer = new Serializer($normalizers, $encoders);

.. _serializer-built-in-normalizers:

Serializer Normalizers
----------------------

By default, the serializer service is configured with the following
normalizers (in order of priority):

:class:`Symfony\\Component\\Serializer\\Normalizer\\UnwrappingDenormalizer`
    Can be used to only denormalize a part of the input, read more about
    this :ref:`later in this article <serializer-unwrapping-denormalizer>`.

:class:`Symfony\\Component\\Serializer\\Normalizer\\ProblemNormalizer`
    Normalizes :class:`Symfony\\Component\\ErrorHandler\\Exception\\FlattenException`
    errors according to the API Problem spec `RFC 7807`_.

:class:`Symfony\\Component\\Serializer\\Normalizer\\UidNormalizer`
    Normalizes objects that extend :class:`Symfony\\Component\\Uid\\AbstractUid`.

    The default normalization format for objects that implement :class:`Symfony\\Component\\Uid\\Uuid`
    is the `RFC 4122`_ format (example: ``d9e7a184-5d5b-11ea-a62a-3499710062d0``).
    The default normalization format for objects that implement :class:`Symfony\\Component\\Uid\\Ulid`
    is the Base 32 format (example: ``01E439TP9XJZ9RPFH3T1PYBCR8``).
    You can change the string format by setting the serializer context option
    ``UidNormalizer::NORMALIZATION_FORMAT_KEY`` to ``UidNormalizer::NORMALIZATION_FORMAT_BASE_58``,
    ``UidNormalizer::NORMALIZATION_FORMAT_BASE_32`` or ``UidNormalizer::NORMALIZATION_FORMAT_RFC_4122``.

    Also it can denormalize ``uuid`` or ``ulid`` strings to :class:`Symfony\\Component\\Uid\\Uuid`
    or :class:`Symfony\\Component\\Uid\\Ulid`. The format does not matter.

:class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeNormalizer`
    This normalizes between :phpclass:`DateTimeInterface` objects (e.g.
    :phpclass:`DateTime` and :phpclass:`DateTimeImmutable`) and strings,
    integers or floats.

    :phpclass:`DateTime` and :phpclass:`DateTimeImmutable`) into strings,
    integers or floats. By default, it converts them to strings using the
    `RFC 3339`_ format. Use ``DateTimeNormalizer::FORMAT_KEY`` and
    ``DateTimeNormalizer::TIMEZONE_KEY`` to change the format.

    To convert the objects to integers or floats, set the serializer
    context option ``DateTimeNormalizer::CAST_KEY`` to ``int`` or
    ``float``.

    .. versionadded:: 7.1

        The ``DateTimeNormalizer::CAST_KEY`` context option was introduced in Symfony 7.1.

:class:`Symfony\\Component\\Serializer\\Normalizer\\ConstraintViolationListNormalizer`
    This normalizer converts objects that implement
    :class:`Symfony\\Component\\Validator\\ConstraintViolationListInterface`
    into a list of errors according to the `RFC 7807`_ standard.

:class:`Symfony\\Component\\Serializer\\Normalizer\\DateTimeZoneNormalizer`
    This normalizer converts between :phpclass:`DateTimeZone` objects and strings that
    represent the name of the timezone according to the `list of PHP timezones`_.

:class:`Symfony\\Component\\Serializer\\Normalizer\\DateIntervalNormalizer`
    This normalizes between :phpclass:`DateInterval` objects and strings.
    By default, the ``P%yY%mM%dDT%hH%iM%sS`` format is used. Use the
    ``DateIntervalNormalizer::FORMAT_KEY`` option to change this.

:class:`Symfony\\Component\\Serializer\\Normalizer\\FormErrorNormalizer`
    This normalizer works with classes that implement
    :class:`Symfony\\Component\\Form\\FormInterface`.

    It will get errors from the form and normalize them according to the
    API Problem spec `RFC 7807`_.

:class:`Symfony\\Component\\Serializer\\Normalizer\\TranslatableNormalizer`
    This normalizer converts objects implementing :class:`Symfony\\Contracts\\Translation\\TranslatableInterface`
    to a translated string using the :doc:`translator </translation>`.

    You can define the locale to use to translate the object by setting the
    ``TranslatableNormalizer::NORMALIZATION_LOCALE_KEY`` context option.

:class:`Symfony\\Component\\Serializer\\Normalizer\\BackedEnumNormalizer`
    This normalizer converts between :phpclass:`BackedEnum` enums and
    strings or integers.

    By default, an exception is thrown when data is not a valid backed enumeration. If you
    want ``null`` instead, you can set the ``BackedEnumNormalizer::ALLOW_INVALID_VALUES`` option.

:class:`Symfony\\Component\\Serializer\\Normalizer\\DataUriNormalizer`
    This normalizer converts between :phpclass:`SplFileInfo` objects and a
    `data URI`_ string (``data:...``) such that files can be embedded into
    serialized data.

:class:`Symfony\\Component\\Serializer\\Normalizer\\JsonSerializableNormalizer`
    This normalizer works with classes that implement :phpclass:`JsonSerializable`.

    It will call the :phpmethod:`JsonSerializable::jsonSerialize` method and
    then further normalize the result. This means that nested
    :phpclass:`JsonSerializable` classes will also be normalized.

    This normalizer is particularly helpful when you want to gradually migrate
    from an existing codebase using simple :phpfunction:`json_encode` to the Symfony
    Serializer by allowing you to mix which normalizers are used for which classes.

    Unlike with :phpfunction:`json_encode` circular references can be handled.

:class:`Symfony\\Component\\Serializer\\Normalizer\\ArrayDenormalizer`
    This denormalizer converts an array of arrays to an array of objects
    (with the given type). See :ref:`Handling Arrays <serializer-handling-arrays>`.

:class:`Symfony\\Component\\Serializer\\Normalizer\\ObjectNormalizer`
    This is the most powerful default normalizer and used for any object
    that could not be normalized by the other normalizers.

    It leverages the :doc:`PropertyAccess Component </components/property_access>`
    to read and write in the object. This allows it to access properties
    directly or using getters, setters, hassers, issers, canners, adders and
    removers. Names are generated by removing the ``get``, ``set``,
    ``has``, ``is``, ``add`` or ``remove`` prefix from the method name and
    transforming the first letter to lowercase (e.g. ``getFirstName()`` ->
    ``firstName``).

    During denormalization, it supports using the constructor as well as
    the discovered methods.

.. danger::

    Always make sure the ``DateTimeNormalizer`` is registered when
    serializing the ``DateTime`` or ``DateTimeImmutable`` classes to avoid
    excessive memory usage and exposing internal details.

Built-in Normalizers
~~~~~~~~~~~~~~~~~~~~

Besides the normalizers registered by default (see previous section), the
serializer component also provides some extra normalizers.You can register
these by defining a service and tag it with :ref:`serializer.normalizer <reference-dic-tags-serializer-normalizer>`.
For instance, to use the ``CustomNormalizer`` you have to define a service
like:

.. configuration-block::

    .. code-block:: yaml

        # config/services.yaml
        services:
            # ...

            # if you're using autoconfigure, the tag will be automatically applied
            Symfony\Component\Serializer\Normalizer\CustomNormalizer:
                tags:
                    # register the normalizer with a high priority (called earlier)
                    - { name: 'serializer.normalizer', priority: 500 }

    .. code-block:: xml

        <!-- config/services.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <container xmlns="http://symfony.com/schema/dic/services"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/services
                https://symfony.com/schema/dic/services/services-1.0.xsd">

            <services>
                <!-- ... -->

                <!-- if you're using autoconfigure, the tag will be automatically applied -->
                <service id="Symfony\Component\Serializer\Normalizer\CustomNormalizer">
                    <!-- register the normalizer with a high priority (called earlier) -->
                    <tag name="serializer.normalizer"
                        priority="500"
                    />
                </service>
            </services>
        </container>

    .. code-block:: php

        // config/services.php
        namespace Symfony\Component\DependencyInjection\Loader\Configurator;

        use Symfony\Component\Serializer\Normalizer\CustomNormalizer;

        return function(ContainerConfigurator $container) {
            // ...

            // if you're using autoconfigure, the tag will be automatically applied
            $services->set(CustomNormalizer::class)
                // register the normalizer with a high priority (called earlier)
                ->tag('serializer.normalizer', [
                    'priority' => 500,
                ])
            ;
        };

:class:`Symfony\\Component\\Serializer\\Normalizer\\CustomNormalizer`
    This normalizer calls a method on the PHP object when normalizing. The
    PHP object must implement :class:`Symfony\\Component\\Serializer\\Normalizer\\NormalizableInterface`
    and/or :class:`Symfony\\Component\\Serializer\\Normalizer\\DenormalizableInterface`.

:class:`Symfony\\Component\\Serializer\\Normalizer\\GetSetMethodNormalizer`
    This normalizer is an alternative to the default ``ObjectNormalizer``.
    It reads the content of the class by calling the "getters" (public
    methods starting with ``get``, ``has``, ``is`` or ``can``). It will
    denormalize data by calling the constructor and the "setters" (public
    methods starting with ``set``).

    Objects are normalized to a map of property names and values (names are
    generated by removing the ``get`` prefix from the method name and transforming
    the first letter to lowercase; e.g. ``getFirstName()`` -> ``firstName``).

:class:`Symfony\\Component\\Serializer\\Normalizer\\PropertyNormalizer`
    This is yet another alternative to the ``ObjectNormalizer``. This
    normalizer directly reads and writes public properties as well as
    **private and protected** properties (from both the class and all of
    its parent classes) by using `PHP reflection`_. It supports calling the
    constructor during the denormalization process.

    Objects are normalized to a map of property names to property values.

    You can also limit the normalizer to only use properties with a specific
    visibility (e.g. only public properties) using the
    ``PropertyNormalizer::NORMALIZE_VISIBILITY`` context option. You can set it
    to any combination of the ``PropertyNormalizer::NORMALIZE_PUBLIC``,
    ``PropertyNormalizer::NORMALIZE_PROTECTED`` and
    ``PropertyNormalizer::NORMALIZE_PRIVATE`` constants::

        use Symfony\Component\Serializer\Normalizer\PropertyNormalizer;
        // ...

        $json = $serializer->serialize($person, 'json', [
            // only serialize public properties
            PropertyNormalizer::NORMALIZE_VISIBILITY => PropertyNormalizer::NORMALIZE_PUBLIC,

            // serialize public and protected properties
            PropertyNormalizer::NORMALIZE_VISIBILITY => PropertyNormalizer::NORMALIZE_PUBLIC | PropertyNormalizer::NORMALIZE_PROTECTED,
        ]);

Debugging the Serializer
------------------------

Use the ``debug:serializer`` command to dump the serializer metadata of a
given class:

.. code-block:: terminal

    $ php bin/console debug:serializer 'App\Entity\Book'

        App\Entity\Book
        ---------------

        +----------+------------------------------------------------------------+
        | Property | Options                                                    |
        +----------+------------------------------------------------------------+
        | name     | [                                                          |
        |          |   "groups" => [                                            |
        |          |       "book:read",                                         |
        |          |       "book:write",                                        |
        |          |   ],                                                       |
        |          |   "maxDepth" => 1,                                         |
        |          |   "serializedName" => "book_name",                         |
        |          |   "serializedPath" => null,                                |
        |          |   "ignore" => false,                                       |
        |          |   "normalizationContexts" => [],                           |
        |          |   "denormalizationContexts" => []                          |
        |          | ]                                                          |
        | isbn     | [                                                          |
        |          |   "groups" => [                                            |
        |          |       "book:read",                                         |
        |          |   ],                                                       |
        |          |   "maxDepth" => null,                                      |
        |          |   "serializedName" => null,                                |
        |          |   "serializedPath" => "[data][isbn]",                      |
        |          |   "ignore" => false,                                       |
        |          |   "normalizationContexts" => [],                           |
        |          |   "denormalizationContexts" => []                          |
        |          | ]                                                          |
        +----------+------------------------------------------------------------+

Advanced Serialization
----------------------

Skipping ``null`` Values
~~~~~~~~~~~~~~~~~~~~~~~~

By default, the Serializer will preserve properties containing a ``null`` value.
You can change this behavior by setting the ``AbstractObjectNormalizer::SKIP_NULL_VALUES`` context option
to ``true``::

    class Person
    {
        public string $name = 'Jane Doe';
        public ?string $gender = null;
    }

    $jsonContent = $serializer->serialize(new Person(), 'json', [
        AbstractObjectNormalizer::SKIP_NULL_VALUES => true,
    ]);
    // $jsonContent contains {"name":"Jane Doe"}

Handling Uninitialized Properties
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In PHP, typed properties have an ``uninitialized`` state which is different
from the default ``null`` of untyped properties. When you try to access a typed
property before giving it an explicit value, you get an error.

To avoid the serializer throwing an error when serializing or normalizing
an object with uninitialized properties, by default the ``ObjectNormalizer``
catches these errors and ignores such properties.

You can disable this behavior by setting the
``AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES`` context option to
``false``::

    class Person {
        public string $name = 'Jane Doe';
        public string $phoneNumber; // uninitialized
    }

    $jsonContent = $normalizer->serialize(new Dummy(), 'json', [
        AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES => false,
    ]);
    // throws Symfony\Component\PropertyAccess\Exception\UninitializedPropertyException
    // as the ObjectNormalizer cannot read uninitialized properties

.. note::

    Using :class:`Symfony\\Component\\Serializer\\Normalizer\\PropertyNormalizer`
    or :class:`Symfony\\Component\\Serializer\\Normalizer\\GetSetMethodNormalizer`
    with ``AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES`` context
    option set to ``false`` will throw an ``\Error`` instance if the given
    object has uninitialized properties as the normalizers cannot read them
    (directly or via getter/isser methods).

.. _component-serializer-handling-circular-references:

Handling Circular References
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Circular references are common when dealing with associated objects::

    class Organization
    {
        public function __construct(
            private string $name,
            private array $members = []
        ) {
        }

        public function getName(): string
        {
            return $this->name;
        }

        public function addMember(Member $member): void
        {
            $this->members[] = $member;
        }

        public function getMembers(): array
        {
            return $this->members;
        }
    }

    class Member
    {
        private Organization $organization;

        public function __construct(
            private string $name
        ) {
        }

        public function getName(): string
        {
            return $this->name;
        }

        public function setOrganization(Organization $organization): void
        {
            $this->organization = $organization;
        }

        public function getOrganization(): Organization
        {
            return $this->organization;
        }
    }

To avoid infinite loops, the normalizers throw a
:class:`Symfony\\Component\\Serializer\\Exception\\CircularReferenceException`
when such a case is encountered::

    $organization = new Organization('Les-Tilleuls.coop');
    $member = new Member('Kévin');

    $organization->addMember($member);
    $member->setOrganization($organization);

    $jsonContent = $serializer->serialize($organization, 'json');
    // throws a CircularReferenceException

The key ``circular_reference_limit`` in the context sets the number of
times it will serialize the same object before considering it a circular
reference. The default value is ``1``.

Instead of throwing an exception, circular references can also be handled
by custom callables. This is especially useful when serializing entities
having unique identifiers::

    use Symfony\Component\Serializer\Exception\CircularReferenceException;

    $context = [
        AbstractNormalizer::CIRCULAR_REFERENCE_HANDLER => function (object $object, ?string $format, array $context): string {
            if (!$object instanceof Organization) {
                throw new CircularReferenceException('A circular reference has been detected when serializing the object of class "'.get_debug_type($object).'".');
            }

            // serialize the nested Organization with only the name (and not the members)
            return $object->getName();
        },
    ];

    $jsonContent = $serializer->serialize($organization, 'json', $context);
    // $jsonContent contains {"name":"Les-Tilleuls.coop","members":[{"name":"K\u00e9vin", organization: "Les-Tilleuls.coop"}]}

.. _serializer_handling-serialization-depth:

Handling Serialization Depth
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The serializer can also detect nested objects of the same class and limit
the serialization depth. This is useful for tree structures, where the same
object is nested multiple times.

For instance, assume a data structure of a family tree::

    // ...
    class Person
    {
        // ...

        public function __construct(
            private string $name,
            private ?self $mother
        ) {
        }

        public function getName(): string
        {
            return $this->name;
        }

        public function getMother(): ?self
        {
            return $this->mother;
        }

        // ...
    }

    // ...
    $greatGrandmother = new Person('Elizabeth', null);
    $grandmother = new Person('Jane', $greatGrandmother);
    $mother = new Person('Sophie', $grandmother);
    $child = new Person('Joe', $mother);

You can specify the maximum depth for a given property. For instance, you
can set the max depth to ``1`` to always only serialize someone's mother
(and not their grandmother, etc.):

.. configuration-block::

    .. code-block:: php-attributes

        // src/Model/Person.php
        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\MaxDepth;

        class Person
        {
            #[MaxDepth(1)]
            private ?self $mother;

            // ...
        }

    .. code-block:: yaml

        # config/serializer/person.yaml
        App\Model\Person:
            attributes:
                mother:
                    max_depth: 1

    .. code-block:: xml

        <!-- config/serializer/person.xml -->
        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\Person">
                <attribute name="mother" max-depth="1"/>
            </class>
        </serializer>

To limit the serialization depth, you must set the
``AbstractObjectNormalizer::ENABLE_MAX_DEPTH`` key to ``true`` in the
context (or the default context specified in ``framework.yaml``)::

    // ...
    $greatGrandmother = new Person('Elizabeth', null);
    $grandmother = new Person('Jane', $greatGrandmother);
    $mother = new Person('Sophie', $grandmother);
    $child = new Person('Joe', $mother);

    $jsonContent = $serializer->serialize($child, null, [
        AbstractObjectNormalizer::ENABLE_MAX_DEPTH => true
    ]);
    // $jsonContent contains {"name":"Joe","mother":{"name":"Sophie"}}

You can also configure a custom callable that is used when the maximum
depth is reached. This can be used to for instance return the unique
identifier of the next nested object, instead of omitting the property::

    use Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer;
    // ...

    $greatGrandmother = new Person('Elizabeth', null);
    $grandmother = new Person('Jane', $greatGrandmother);
    $mother = new Person('Sophie', $grandmother);
    $child = new Person('Joe', $mother);

    // all callback parameters are optional (you can omit the ones you don't use)
    $maxDepthHandler = function (object $innerObject, object $outerObject, string $attributeName, ?string $format = null, array $context = []): string {
        // return only the name of the next person in the tree
        return $innerObject instanceof Person ? $innerObject->getName() : null;
    };

    $jsonContent = $serializer->serialize($child, null, [
        AbstractObjectNormalizer::ENABLE_MAX_DEPTH => true,
        AbstractObjectNormalizer::MAX_DEPTH_HANDLER => $maxDepthHandler,
    ]);
    // $jsonContent contains {"name":"Joe","mother":{"name":"Sophie","mother":"Jane"}}

Using Callbacks to Serialize Properties with Object Instances
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When serializing, you can set a callback to format a specific object
property. This can be used instead of
:ref:`defining the context for a group <serializer-context-group>`::

    $person = new Person('cordoval', 34);
    $person->setCreatedAt(new \DateTime('now'));

    $context = [
        AbstractNormalizer::CALLBACKS => [
            // all callback parameters are optional (you can omit the ones you don't use)
            'createdAt' => function (object $attributeValue, object $object, string $attributeName, ?string $format = null, array $context = []) {
                return $attributeValue instanceof \DateTime ? $attributeValue->format(\DateTime::ATOM) : '';
            },
        ],
    ];
    $jsonContent = $serializer->serialize($person, 'json', $context);
    // $jsonContent contains {"name":"cordoval","age":34,"createdAt":"2014-03-22T09:43:12-0500"}

Advanced Deserialization
------------------------

Require all Properties
~~~~~~~~~~~~~~~~~~~~~~

By default, the Serializer will add ``null`` to nullable properties when
the parameters for those are not provided. You can change this behavior by
setting the ``AbstractNormalizer::REQUIRE_ALL_PROPERTIES`` context option
to ``true``::

    class Person
    {
        public function __construct(
            public string $firstName,
            public ?string $lastName,
        ) {
        }
    }

    // ...
    $data = ['firstName' => 'John'];
    $person = $serializer->deserialize($data, Person::class, 'json', [
        AbstractNormalizer::REQUIRE_ALL_PROPERTIES => true,
    ]);
    // throws Symfony\Component\Serializer\Exception\MissingConstructorArgumentException

Collecting Type Errors While Denormalizing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When denormalizing a payload to an object with typed properties, you'll get an
exception if the payload contains properties that don't have the same type as
the object.

Use the ``COLLECT_DENORMALIZATION_ERRORS`` option to collect all exceptions
at once, and to get the object partially denormalized::

    try {
        $person = $serializer->deserialize($jsonString, Person::class, 'json', [
            DenormalizerInterface::COLLECT_DENORMALIZATION_ERRORS => true,
        ]);
    } catch (PartialDenormalizationException $e) {
        $violations = new ConstraintViolationList();

        /** @var NotNormalizableValueException $exception */
        foreach ($e->getErrors() as $exception) {
            $message = sprintf('The type must be one of "%s" ("%s" given).', implode(', ', $exception->getExpectedTypes()), $exception->getCurrentType());
            $parameters = [];
            if ($exception->canUseMessageForUser()) {
                $parameters['hint'] = $exception->getMessage();
            }
            $violations->add(new ConstraintViolation($message, '', $parameters, null, $exception->getPath(), null));
        }

        // ... return violation list to the user
    }

.. _serializer-populate-existing-object:

Deserializing in an Existing Object
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The serializer can also be used to update an existing object. You can do
this by configuring the ``object_to_populate`` serializer context option::

    use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;

    // ...
    $person = new Person('Jane Doe', 59);

    $serializer->deserialize($jsonData, Person::class, 'json', [
        AbstractNormalizer::OBJECT_TO_POPULATE => $person,
    ]);
    // instead of returning a new object, $person is updated instead

.. note::

    The ``AbstractNormalizer::OBJECT_TO_POPULATE`` option is only used for
    the top level object. If that object is the root of a tree structure,
    all child elements that exist in the normalized data will be re-created
    with new instances.

    When the ``AbstractObjectNormalizer::DEEP_OBJECT_TO_POPULATE`` context
    option is set to ``true``, existing children of the root ``OBJECT_TO_POPULATE``
    are updated from the normalized data, instead of the denormalizer
    re-creating them. This only works for single child objects, not for
    arrays of objects. Those will still be replaced when present in the
    normalized data.

.. _serializer_interfaces-and-abstract-classes:

Deserializing Interfaces and Abstract Classes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When working with associated objects, a property sometimes reference an
interface or abstract class. When deserializing these properties, the
Serializer has to know which concrete class to initialize. This is done
using a *discriminator class mapping*.

Imagine there is an ``InvoiceItemInterface`` that is implemented by the
``Product`` and ``Shipping`` objects. When serializing an object, the
serializer will add an extra "discriminator attribute". This contains
either ``product`` or ``shipping``. The discriminator class map maps
these type names to the real PHP class name when deserializing:

.. configuration-block::

    .. code-block:: php-attributes

        namespace App\Model;

        use Symfony\Component\Serializer\Attribute\DiscriminatorMap;

        #[DiscriminatorMap(
            typeProperty: 'type',
            mapping: [
                'product' => Product::class,
                'shipping' => Shipping::class,
            ]
        )]
        interface InvoiceItemInterface
        {
            // ...
        }

    .. code-block:: yaml

        App\Model\InvoiceItemInterface:
            discriminator_map:
                type_property: type
                mapping:
                    product: 'App\Model\Product'
                    shipping: 'App\Model\Shipping'

    .. code-block:: xml

        <?xml version="1.0" encoding="UTF-8" ?>
        <serializer xmlns="http://symfony.com/schema/dic/serializer-mapping"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/serializer-mapping
                https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
        >
            <class name="App\Model\InvoiceItemInterface">
                <discriminator-map type-property="type">
                    <mapping type="product" class="App\Model\Product"/>
                    <mapping type="shipping" class="App\Model\Shipping"/>
                </discriminator-map>
            </class>
        </serializer>

With the discriminator map configured, the serializer can now pick the
correct class for properties typed as ``InvoiceItemInterface``::

.. configuration-block::

    .. code-block:: php-symfony

        class InvoiceLine
        {
            public function __construct(
                private InvoiceItemInterface $invoiceItem
            ) {
                $this->invoiceItem = $invoiceItem;
            }

            public function getInvoiceItem(): InvoiceItemInterface
            {
                return $this->invoiceItem;
            }

            // ...
        }

        // ...
        $invoiceLine = new InvoiceLine(new Product());

        $jsonString = $serializer->serialize($invoiceLine, 'json');
        // $jsonString contains {"type":"product",...}

        $invoiceLine = $serializer->deserialize($jsonString, InvoiceLine::class, 'json');
        // $invoiceLine contains new InvoiceLine(new Product(...))

    .. code-block:: php-standalone

        // ...
        use Symfony\Component\Serializer\Mapping\ClassDiscriminatorFromClassMetadata;
        use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
        use Symfony\Component\Serializer\Mapping\Loader\AttributeLoader;
        use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
        use Symfony\Component\Serializer\Serializer;

        class InvoiceLine
        {
            public function __construct(
                private InvoiceItemInterface $invoiceItem
            ) {
                $this->invoiceItem = $invoiceItem;
            }

            public function getInvoiceItem(): InvoiceItemInterface
            {
                return $this->invoiceItem;
            }

            // ...
        }

        // ...

        // Configure a loader to retrieve mapping information like DiscriminatorMap.
        // E.g. when using PHP attributes:
        $classMetadataFactory = new ClassMetadataFactory(new AttributeLoader());
        $discriminator = new ClassDiscriminatorFromClassMetadata($classMetadataFactory);
        $normalizers = [
            new ObjectNormalizer($classMetadataFactory, null, null, null, $discriminator),
        ];

        $serializer = new Serializer($normalizers, $encoders);

        $invoiceLine = new InvoiceLine(new Product());

        $jsonString = $serializer->serialize($invoiceLine, 'json');
        // $jsonString contains {"type":"product",...}

        $invoiceLine = $serializer->deserialize($jsonString, InvoiceLine::class, 'json');
        // $invoiceLine contains new InvoiceLine(new Product(...))

.. _serializer-unwrapping-denormalizer:

Deserializing Input Partially (Unwrapping)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The serializer will always deserialize the complete input string into PHP
values. When connecting with third party APIs, you often only need a
specific part of the returned response.

To avoid deserializing the whole response, you can use the
:class:`Symfony\\Component\\Serializer\\Normalizer\\UnwrappingDenormalizer`
and "unwrap" the input data::

    $jsonData = '{"result":"success","data":{"person":{"name": "Jane Doe","age":57}}}';
    $data = $serialiser->deserialize($jsonData, Object::class, [
        UnwrappingDenormalizer::UNWRAP_PATH => '[data][person]',
    ]);
    // $data is Person(name: 'Jane Doe', age: 57)

The ``unwrap_path`` is a :ref:`property path <property-access-reading-arrays>`
of the PropertyAccess component, applied on the denormalized array.

Handling Constructor Arguments
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If the class constructor defines arguments, as usually happens with
`Value Objects`_, the serializer will match the parameter names with the
deserialized attributes. If some parameters are missing, a
:class:`Symfony\\Component\\Serializer\\Exception\\MissingConstructorArgumentsException`
is thrown.

In these cases, use the ``default_constructor_arguments`` context option to
define default values for the missing parameters::

    use App\Model\Person;
    use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;
    // ...

    $jsonData = '{"age":39,"name":"Jane Doe"}';
    $person = $serializer->deserialize($jsonData, Person::class, 'json', [
        AbstractNormalizer::DEFAULT_CONSTRUCTOR_ARGUMENTS => [
            Person::class => ['sportsperson' => true],
        ],
    ]);
    // $person is Person(name: 'Jane Doe', age: 39, sportsperson: true);

Recursive Denormalization and Type Safety
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When a ``PropertyTypeExtractor`` is available, the normalizer will also
check that the data to denormalize matches the type of the property (even
for primitive types). For instance, if a ``string`` is provided, but the
type of the property is ``int``, an
:class:`Symfony\\Component\\Serializer\\Exception\\UnexpectedValueException`
will be thrown. The type enforcement of the properties can be disabled by
setting the serializer context option
``ObjectNormalizer::DISABLE_TYPE_ENFORCEMENT`` to ``true``.

Handling Boolean Values
~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 7.1

    The ``AbstractNormalizer::FILTER_BOOL`` context option was introduced in Symfony 7.1.

PHP considers many different values as true or false. For example, the
strings ``true``, ``1``, and ``yes`` are considered true, while
``false``, ``0``, and ``no`` are considered false.

When deserializing, the Serializer component can take care of this
automatically. This can be done by using the ``AbstractNormalizer::FILTER_BOOL``
context option::

    use Symfony\Component\Serializer\Normalizer\AbstractNormalizer;
    // ...

    $person = $serializer->denormalize(['sportsperson' => 'yes'], Person::class, context: [
        AbstractNormalizer::FILTER_BOOL => true
    ]);
    // $person contains a Person instance with sportsperson set to true

This context makes the deserialization process behave like the
:phpfunction:`filter_var` function with the ``FILTER_VALIDATE_BOOL`` flag.

.. _serializer-enabling-metadata-cache:

Configuring the Metadata Cache
------------------------------

The metadata for the serializer is automatically cached to enhance application
performance. By default, the serializer uses the ``cache.system`` cache pool
which is configured using the :ref:`cache.system <reference-cache-system>`
option.

Going Further with the Serializer
---------------------------------

.. toctree::
    :glob:
    :maxdepth: 1

    serializer/*

.. _`JMS serializer`: https://github.com/schmittjoh/serializer
.. _`API Platform`: https://api-platform.com
.. _`JSON-LD`: https://json-ld.org
.. _`Hydra Core Vocabulary`: https://www.hydra-cg.com/
.. _`OpenAPI`: https://www.openapis.org
.. _`GraphQL`: https://graphql.org
.. _`JSON:API`: https://jsonapi.org
.. _`HAL`: https://stateless.group/hal_specification.html
.. _`RFC 7807`: https://tools.ietf.org/html/rfc7807
.. _`RFC 4122`: https://tools.ietf.org/html/rfc4122
.. _`RFC 3339`: https://tools.ietf.org/html/rfc3339#section-5.8
.. _`list of PHP timezones`: https://www.php.net/manual/en/timezones.php
.. _`data URI`: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
.. _`PHP reflection`: https://php.net/manual/en/book.reflection.php
.. _`Value Objects`: https://en.wikipedia.org/wiki/Value_object
