The Serializer Component

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Read the updated version of this page for Symfony 6.3 (the current stable version).

The Serializer Component

The Serializer component is meant to be used to turn objects into a specific format (XML, JSON, YAML, ...) and the other way around.

In order to do so, the Serializer component follows the following schema.

As you can see in the picture above, an array is used as an intermediary between objects and serialized contents. This way, encoders will only deal with turning specific formats into arrays and vice versa. The same way, Normalizers will deal with turning specific objects into arrays and vice versa.

Serialization is a complex topic. This component may not cover all your use cases out of the box, but it can be useful for developing tools to serialize and deserialize your objects.

Installation

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        $ composer require symfony/serializer
    

Alternatively, you can clone the https://github.com/symfony/serializer repository.

Note

If you install this component outside of a Symfony application, you must require the vendor/autoload.php file in your code to enable the class autoloading mechanism provided by Composer. Read this article for more details.

To use the ObjectNormalizer, the PropertyAccess component must also be installed.

Usage

Serializing an Object

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

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        namespace App\Model;

class Person
{
    private $age;
    private $name;
    private $sportsperson;
    private $createdAt;

    // Getters
    public function getName()
    {
        return $this->name;
    }

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

    public function getCreatedAt()
    {
        return $this->createdAt;
    }

    // Issers
    public function isSportsperson()
    {
        return $this->sportsperson;
    }

    // Setters
    public function setName($name)
    {
        $this->name = $name;
    }

    public function setAge($age)
    {
        $this->age = $age;
    }

    public function setSportsperson($sportsperson)
    {
        $this->sportsperson = $sportsperson;
    }

    public function setCreatedAt($createdAt)
    {
        $this->createdAt = $createdAt;
    }
}
    

Now, if you want to serialize this object into JSON, you only need to use the Serializer service created before:

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        $person = new App\Model\Person();
$person->setName('foo');
$person->setAge(99);
$person->setSportsperson(false);

$jsonContent = $serializer->serialize($person, 'json');

// $jsonContent contains {"name":"foo","age":99,"sportsperson":false,"createdAt":null}

echo $jsonContent; // or return it in a Response
    

The first parameter of the serialize() is the object to be serialized and the second is used to choose the proper encoder, in this case JsonEncoder.

Deserializing an Object

You'll now learn how to do the exact opposite. This time, the information of the Person class would be encoded in XML format:

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        use App\Model\Person;

$data = <<<EOF
<person>
    <name>foo</name>
    <age>99</age>
    <sportsperson>false</sportsperson>
</person>
EOF;

$person = $serializer->deserialize($data, Person::class, 'xml');
    

In this case, deserialize() needs three parameters:

The information to be decoded
The name of the class this information will be decoded to
The encoder used to convert that information into an array

By default, additional attributes that are not mapped to the denormalized object will be ignored by the Serializer component. If you prefer to throw an exception when this happens, set the allow_extra_attributes context option to false and provide an object that implements ClassMetadataFactoryInterface when constructing the normalizer:

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        $data = <<<EOF
<person>
    <name>foo</name>
    <age>99</age>
    <city>Paris</city>
</person>
EOF;

// this will throw a Symfony\Component\Serializer\Exception\ExtraAttributesException
// because "city" is not an attribute of the Person class
$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
$normalizer = new ObjectNormalizer($classMetadataFactory);
$serializer = new Serializer([$normalizer]);
$person = $serializer->deserialize($data, 'App\Model\Person', 'xml', [
    'allow_extra_attributes' => false,
]);
    

Deserializing in an Existing Object

The serializer can also be used to update an existing object:

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        // ...
$person = new Person();
$person->setName('bar');
$person->setAge(99);
$person->setSportsperson(true);

$data = <<<EOF
<person>
    <name>foo</name>
    <age>69</age>
</person>
EOF;

$serializer->deserialize($data, Person::class, 'xml', ['object_to_populate' => $person]);
// $person = App\Model\Person(name: 'foo', age: '69', sportsperson: true)
    

This is a common need when working with an ORM.

Attributes Groups

Sometimes, you want to serialize different sets of attributes from your entities. Groups are a handy way to achieve this need.

Assume you have the following plain-old-PHP object:

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        namespace Acme;

class MyObj
{
    public $foo;

    private $bar;

    public function getBar()
    {
        return $this->bar;
    }

    public function setBar($bar)
    {
        return $this->bar = $bar;
    }
}
    

The definition of serialization can be specified using annotations, XML or YAML. The ClassMetadataFactory that will be used by the normalizer must be aware of the format to use.

Initialize the ClassMetadataFactory like the following:

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        use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
// For annotations
use Doctrine\Common\Annotations\AnnotationReader;
use Symfony\Component\Serializer\Mapping\Loader\AnnotationLoader;
// For XML
// use Symfony\Component\Serializer\Mapping\Loader\XmlFileLoader;
// For YAML
// use Symfony\Component\Serializer\Mapping\Loader\YamlFileLoader;

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
// For XML
// $classMetadataFactory = new ClassMetadataFactory(new XmlFileLoader('/path/to/your/definition.xml'));
// For YAML
// $classMetadataFactory = new ClassMetadataFactory(new YamlFileLoader('/path/to/your/definition.yaml'));
    

Then, create your groups definition:

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        namespace Acme;

use Symfony\Component\Serializer\Annotation\Groups;

class MyObj
{
    /**
     * @Groups({"group1", "group2"})
     */
    public $foo;

    /**
     * @Groups("group3")
     */
    public function getBar() // is* methods are also supported
    {
        return $this->bar;
    }

    // ...
}
    

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        Acme\MyObj:
    attributes:
        foo:
            groups: ['group1', 'group2']
        bar:
            groups: ['group3']
    

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        <?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
        http://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
>
    <class name="Acme\MyObj">
        <attribute name="foo">
            <group>group1</group>
            <group>group2</group>
        </attribute>

        <attribute name="bar">
            <group>group3</group>
        </attribute>
    </class>
</serializer>
    

You are now able to serialize only attributes in the groups you want:

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

$obj = new MyObj();
$obj->foo = 'foo';
$obj->setBar('bar');

$normalizer = new ObjectNormalizer($classMetadataFactory);
$serializer = new Serializer([$normalizer]);

$data = $serializer->normalize($obj, null, ['groups' => ['group1']]);
// $data = ['foo' => 'foo'];

$obj2 = $serializer->denormalize(
    ['foo' => 'foo', 'bar' => 'bar'],
    'MyObj',
    null,
    ['groups' => ['group1', 'group3']]
);
// $obj2 = MyObj(foo: 'foo', bar: 'bar')
    

Note

In order to use the annotation loader, you should have installed the doctrine/annotations and doctrine/cache packages with Composer.

Tip

Annotation classes aren't loaded automatically, so you must load them using a class loader like this:

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        use Composer\Autoload\ClassLoader;
use Doctrine\Common\Annotations\AnnotationRegistry;

/** @var ClassLoader $loader */
$loader = require __DIR__.'/../vendor/autoload.php';

AnnotationRegistry::registerLoader([$loader, 'loadClass']);

return $loader;
    

Selecting Specific Attributes

It is also possible to serialize only a set of specific attributes:

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

class User
{
    public $familyName;
    public $givenName;
    public $company;
}

class Company
{
    public $name;
    public $address;
}

$company = new Company();
$company->name = 'Les-Tilleuls.coop';
$company->address = 'Lille, France';

$user = new User();
$user->familyName = 'Dunglas';
$user->givenName = 'Kévin';
$user->company = $company;

$serializer = new Serializer([new ObjectNormalizer()]);

$data = $serializer->normalize($user, null, ['attributes' => ['familyName', 'company' => ['name']]]);
// $data = ['familyName' => 'Dunglas', 'company' => ['name' => 'Les-Tilleuls.coop']];
    

Only attributes that are not ignored (see below) are available. If some serialization groups are set, only attributes allowed by those groups can be used.

As for groups, attributes can be selected during both the serialization and deserialization process.

Ignoring Attributes

Note

Using attribute groups instead of the setIgnoredAttributes() method is considered best practice.

As an option, there's a way to ignore attributes from the origin object. To remove those attributes use the setIgnoredAttributes() method on the normalizer definition:

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        use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

$normalizer = new ObjectNormalizer();
$normalizer->setIgnoredAttributes(['age']);
$encoder = new JsonEncoder();

$serializer = new Serializer([$normalizer], [$encoder]);
$serializer->serialize($person, 'json'); // Output: {"name":"foo","sportsperson":false}
    

Converting Property Names when Serializing and Deserializing

Sometimes serialized attributes must be named differently than properties or getter/setter methods of PHP classes.

The Serializer component provides a handy way to translate or map PHP field names to serialized names: The Name Converter System.

Given you have the following object:

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        class Company
{
    public $name;
    public $address;
}
    

And in the serialized form, all attributes must be prefixed by org_ like the following:

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        {"org_name": "Acme Inc.", "org_address": "123 Main Street, Big City"}
    

A custom name converter can handle such cases:

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        use Symfony\Component\Serializer\NameConverter\NameConverterInterface;

class OrgPrefixNameConverter implements NameConverterInterface
{
    public function normalize($propertyName)
    {
        return 'org_'.$propertyName;
    }

    public function denormalize($propertyName)
    {
        // removes 'org_' prefix
        return 'org_' === substr($propertyName, 0, 4) ? substr($propertyName, 4) : $propertyName;
    }
}
    

The custom name converter can be used by passing it as second parameter of any class extending AbstractNormalizer, including GetSetMethodNormalizer and PropertyNormalizer:

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        use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;

$nameConverter = new OrgPrefixNameConverter();
$normalizer = new ObjectNormalizer(null, $nameConverter);

$serializer = new Serializer([$normalizer], [new JsonEncoder()]);

$company = new Company();
$company->name = 'Acme Inc.';
$company->address = '123 Main Street, Big City';

$json = $serializer->serialize($company, 'json');
// {"org_name": "Acme Inc.", "org_address": "123 Main Street, Big City"}
$companyCopy = $serializer->deserialize($json, Company::class, 'json');
// Same data as $company
    

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 (even though the PSR-1 standard doesn't recommend any specific case for property names).

Symfony provides a built-in name converter designed to transform between snake_case and CamelCased styles during serialization and deserialization processes:

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

$normalizer = new ObjectNormalizer(null, new CamelCaseToSnakeCaseNameConverter());

class Person
{
    private $firstName;

    public function __construct($firstName)
    {
        $this->firstName = $firstName;
    }

    public function getFirstName()
    {
        return $this->firstName;
    }
}

$kevin = new Person('Kévin');
$normalizer->normalize($kevin);
// ['first_name' => 'Kévin'];

$anne = $normalizer->denormalize(['first_name' => 'Anne'], 'Person');
// Person object with firstName: 'Anne'
    

Serializing Boolean Attributes

If you are using isser methods (methods prefixed by is, like App\Model\Person::isSportsperson()), the Serializer component will automatically detect and use it to serialize related attributes.

The ObjectNormalizer also takes care of methods starting with has, add and remove.

Using Callbacks to Serialize Properties with Object Instances

When serializing, you can set a callback to format a specific object property:

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

$encoder = new JsonEncoder();
$normalizer = new GetSetMethodNormalizer();

$callback = function ($dateTime) {
    return $dateTime instanceof \DateTime
        ? $dateTime->format(\DateTime::ISO8601)
        : '';
};

$normalizer->setCallbacks(['createdAt' => $callback]);

$serializer = new Serializer([$normalizer], [$encoder]);

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

$serializer->serialize($person, 'json');
// Output: {"name":"cordoval", "age": 34, "createdAt": "2014-03-22T09:43:12-0500"}
    

Normalizers

There are several types of normalizers available:

ObjectNormalizer

This normalizer leverages the PropertyAccess Component to read and write in the object. It means that it can access to properties directly and through getters, setters, hassers, adders and removers. It supports calling the constructor during the denormalization process.

Objects are normalized to a map of property names and values (names are generated removing the get, set, has or remove prefix from the method name and lowercasing the first letter; e.g. getFirstName() -> firstName).

The ObjectNormalizer is the most powerful normalizer. It is configured by default in Symfony applications with the Serializer component enabled.

GetSetMethodNormalizer

This normalizer reads the content of the class by calling the "getters" (public methods starting with "get"). 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 removing the get prefix from the method name and lowercasing the first letter; e.g. getFirstName() -> firstName).

PropertyNormalizer

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). It supports calling the constructor during the denormalization process.

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

JsonSerializableNormalizer

This normalizer works with classes that implement JsonSerializable.

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

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

Unlike with json_encode circular references can be handled.

DateTimeNormalizer

This normalizer converts DateTimeInterface objects (e.g. DateTime and DateTimeImmutable) into strings. By default it uses the RFC3339 format.

DataUriNormalizer

This normalizer converts SplFileInfo objects into a data URI string (data:...) such that files can be embedded into serialized data.

DateIntervalNormalizer

This normalizer converts DateInterval objects into strings. By default it uses the P%yY%mM%dDT%hH%iM%sS format.

ConstraintViolationListNormalizer

This normalizer converts objects that implement ConstraintViolationListInterface into a list of errors according to the RFC 7807 standard.

4.1

The ConstraintViolationListNormalizer was introduced in Symfony 4.1.

Encoders

Encoders turn arrays into formats and vice versa. They implement EncoderInterface for encoding (array to format) and DecoderInterface for decoding (format to array).

You can add new encoders to a Serializer instance by using its second constructor argument:

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        use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Encoder\XmlEncoder;
use Symfony\Component\Serializer\Encoder\JsonEncoder;

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

Built-in Encoders

The Serializer component provides several built-in encoders:

JsonEncoder: This class encodes and decodes data in JSON.
XmlEncoder: This class encodes and decodes data in XML.
YamlEncoder: This encoder encodes and decodes data in YAML. This encoder requires the Yaml Component.
CsvEncoder: This encoder encodes and decodes data in CSV.

All these encoders are enabled by default when using the Serializer component in a Symfony application.

The `JsonEncoder`

The JsonEncoder encodes to and decodes from JSON strings, based on the PHP json_encode and json_decode functions.

The `CsvEncoder`

The CsvEncoder encodes to and decodes from CSV.

You can pass the context key as_collection in order to have the results always as a collection.

4.1

The as_collection option was introduced in Symfony 4.1.

The `XmlEncoder`

This encoder transforms arrays into XML and vice versa.

For example, take an object normalized as following:

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        ['foo' => [1, 2], 'bar' => true];
    

The XmlEncoder will encode this object like that:

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        <?xml version="1.0"?>
<response>
    <foo>1</foo>
    <foo>2</foo>
    <bar>1</bar>
</response>
    

Be aware that this encoder will consider keys beginning with @ as attributes:

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        $encoder = new XmlEncoder();
$encoder->encode(['foo' => ['@bar' => 'value']], 'xml');
// will return:
// <?xml version="1.0"?>
// <response>
//     <foo bar="value" />
// </response>
    

You can pass the context key as_collection in order to have the results always as a collection.

4.1

The as_collection option was introduced in Symfony 4.1.

Tip

XML comments are ignored by default when decoding contents, but this behavior can be changed with the optional $ignoredNodeTypes argument of the XmlEncoder class constructor.

4.1

XML comments are ignored by default starting from Symfony 4.1.

The `YamlEncoder`

This encoder requires the Yaml Component and transforms from and to Yaml.

Handling Circular References

Circular references are common when dealing with entity relations:

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        class Organization
{
    private $name;
    private $members;

    public function setName($name)
    {
        $this->name = $name;
    }

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

    public function setMembers(array $members)
    {
        $this->members = $members;
    }

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

class Member
{
    private $name;
    private $organization;

    public function setName($name)
    {
        $this->name = $name;
    }

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

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

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

To avoid infinite loops, GetSetMethodNormalizer or ObjectNormalizer throw a CircularReferenceException when such a case is encountered:

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        $member = new Member();
$member->setName('Kévin');

$organization = new Organization();
$organization->setName('Les-Tilleuls.coop');
$organization->setMembers([$member]);

$member->setOrganization($organization);

echo $serializer->serialize($organization, 'json'); // Throws a CircularReferenceException
    

The setCircularReferenceLimit() method of this normalizer sets the number of times it will serialize the same object before considering it a circular reference. Its 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:

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        $encoder = new JsonEncoder();
$normalizer = new ObjectNormalizer();

$normalizer->setCircularReferenceHandler(function ($object) {
    return $object->getName();
});

$serializer = new Serializer([$normalizer], [$encoder]);
var_dump($serializer->serialize($org, 'json'));
// {"name":"Les-Tilleuls.coop","members":[{"name":"K\u00e9vin", organization: "Les-Tilleuls.coop"}]}
    

Handling Serialization Depth

The Serializer component is able to detect and limit the serialization depth. It is especially useful when serializing large trees. Assume the following data structure:

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        namespace Acme;

class MyObj
{
    public $foo;

    /**
     * @var self
     */
    public $child;
}

$level1 = new MyObj();
$level1->foo = 'level1';

$level2 = new MyObj();
$level2->foo = 'level2';
$level1->child = $level2;

$level3 = new MyObj();
$level3->foo = 'level3';
$level2->child = $level3;
    

The serializer can be configured to set a maximum depth for a given property. Here, we set it to 2 for the $child property:

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        use Symfony\Component\Serializer\Annotation\MaxDepth;

namespace Acme;

class MyObj
{
    /**
     * @MaxDepth(2)
     */
    public $child;

    // ...
}
    

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        Acme\MyObj:
    attributes:
        child:
            max_depth: 2
    

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        <?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
        http://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
>
    <class name="Acme\MyObj">
        <attribute name="child" max-depth="2" />
    </class>
</serializer>
    

The metadata loader corresponding to the chosen format must be configured in order to use this feature. It is done automatically when using the Serializer component in a Symfony application. When using the standalone component, refer to the groups documentation to learn how to do that.

The check is only done if the enable_max_depth key of the serializer context is set to true. In the following example, the third level is not serialized because it is deeper than the configured maximum depth of 2:

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        $result = $serializer->normalize($level1, null, ['enable_max_depth' => true]);
/*
$result = [
    'foo' => 'level1',
    'child' => [
            'foo' => 'level2',
            'child' => [
                    'child' => null,
                ],
        ],
];
*/
    

Instead of throwing an exception, a custom callable can be executed when the maximum depth is reached. This is especially useful when serializing entities having unique identifiers:

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        use Doctrine\Common\Annotations\AnnotationReader;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Annotation\MaxDepth;
use Symfony\Component\Serializer\Mapping\Factory\ClassMetadataFactory;
use Symfony\Component\Serializer\Mapping\Loader\AnnotationLoader;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

class Foo
{
    public $id;

    /**
     * @MaxDepth(1)
     */
    public $child;
}

$level1 = new Foo();
$level1->id = 1;

$level2 = new Foo();
$level2->id = 2;
$level1->child = $level2;

$level3 = new Foo();
$level3->id = 3;
$level2->child = $level3;

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));
$normalizer = new ObjectNormalizer($classMetadataFactory);
$normalizer->setMaxDepthHandler(function ($foo) {
    return '/foos/'.$foo->id;
});

$serializer = new Serializer([$normalizer]);

$result = $serializer->normalize($level1, null, [ObjectNormalizer::ENABLE_MAX_DEPTH => true]);
/*
$result = [
    'id' => 1,
    'child' => [
        'id' => 2,
        'child' => '/foos/3',
    ],
];
*/
    

4.1

The setMaxDepthHandler() method was introduced in Symfony 4.1.

Handling Arrays

The Serializer component is capable of handling arrays of objects as well. Serializing arrays works just like serializing a single object:

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        use Acme\Person;

$person1 = new Person();
$person1->setName('foo');
$person1->setAge(99);
$person1->setSportsman(false);

$person2 = new Person();
$person2->setName('bar');
$person2->setAge(33);
$person2->setSportsman(true);

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

// $data contains [{"name":"foo","age":99,"sportsman":false},{"name":"bar","age":33,"sportsman":true}]
    

If you want to deserialize such a structure, you need to add the ArrayDenormalizer to the set of normalizers. By appending [] to the type parameter of the deserialize() method, you indicate that you're expecting an array instead of a single object.

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        use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Normalizer\ArrayDenormalizer;
use Symfony\Component\Serializer\Normalizer\GetSetMethodNormalizer;
use Symfony\Component\Serializer\Serializer;

$serializer = new Serializer(
    [new GetSetMethodNormalizer(), new ArrayDenormalizer()],
    [new JsonEncoder()]
);

$data = ...; // The serialized data from the previous example
$persons = $serializer->deserialize($data, 'Acme\Person[]', 'json');
    

The `XmlEncoder`

This encoder transforms arrays into XML and vice versa. For example, take an object normalized as following:

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        ['foo' => [1, 2], 'bar' => true];
    

The XmlEncoder encodes this object as follows:

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        <?xml version="1.0"?>
<response>
    <foo>1</foo>
    <foo>2</foo>
    <bar>1</bar>
</response>
    

The array keys beginning with @ are considered XML attributes:

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        ['foo' => ['@bar' => 'value']];

// is encoded as follows:
// <?xml version="1.0"?>
// <response>
//     <foo bar="value" />
// </response>
    

Use the special # key to define the data of a node:

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        ['foo' => ['@bar' => 'value', '#' => 'baz']];

// is encoded as follows:
// <?xml version="1.0"?>
// <response>
//     <foo bar="value">
//        baz
//     </foo>
// </response>
    

Context

The encode() method defines a third optional parameter called context which defines the configuration options for the XmlEncoder an associative array:

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        $xmlEncoder->encode($array, 'xml', $context);
    

These are the options available:

xml_format_output: If set to true, formats the generated XML with line breaks and indentation.
xml_version: Sets the XML version attribute (default: 1.1).
xml_encoding: Sets the XML encoding attribute (default: utf-8).
xml_standalone: Adds standalone attribute in the generated XML (default: true).
xml_root_node_name: Sets the root node name (default: response).
remove_empty_tags: If set to true, removes all empty tags in the generated XML.

Handling Constructor Arguments

4.1

The default_constructor_arguments option was introduced in Symfony 4.1.

If the class constructor defines arguments, as usually happens with Value Objects, the serializer won't be able to create the object if some arguments are missing. In those cases, use the default_constructor_arguments context option:

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

class MyObj
{
    private $foo;
    private $bar;

    public function __construct($foo, $bar)
    {
        $this->foo = $foo;
        $this->bar = $bar;
    }
}

$normalizer = new ObjectNormalizer($classMetadataFactory);
$serializer = new Serializer([$normalizer]);

$data = $serializer->denormalize(
    ['foo' => 'Hello'],
    'MyObj',
    ['default_constructor_arguments' => [
        'MyObj' => ['foo' => '', 'bar' => ''],
    ]]
);
// $data = new MyObj('Hello', '');
    

Recursive Denormalization and Type Safety

The Serializer component can use the PropertyInfo Component to denormalize complex types (objects). The type of the class' property will be guessed using the provided extractor and used to recursively denormalize the inner data.

When using this component in a Symfony application, all normalizers are automatically configured to use the registered extractors. When using the component standalone, an implementation of PropertyTypeExtractorInterface, (usually an instance of PropertyInfoExtractor) must be passed as the 4th parameter of the ObjectNormalizer:

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        use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
use Symfony\Component\Serializer\Serializer;
use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

namespace Acme;

class ObjectOuter
{
    private $inner;
    private $date;

    public function getInner()
    {
        return $this->inner;
    }

    public function setInner(ObjectInner $inner)
    {
        $this->inner = $inner;
    }

    public function setDate(\DateTimeInterface $date)
    {
        $this->date = $date;
    }

    public function getDate()
    {
        return $this->date;
    }
}

class ObjectInner
{
    public $foo;
    public $bar;
}

$normalizer = new ObjectNormalizer(null, null, null, new ReflectionExtractor());
$serializer = new Serializer([new DateTimeNormalizer(), $normalizer]);

$obj = $serializer->denormalize(
    ['inner' => ['foo' => 'foo', 'bar' => 'bar'], 'date' => '1988/01/21'],
     'Acme\ObjectOuter'
);

dump($obj->getInner()->foo); // 'foo'
dump($obj->getInner()->bar); // 'bar'
dump($obj->getDate()->format('Y-m-d')); // '1988-01-21'
    

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 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.

Serializing Interfaces and Abstract Classes

When dealing with objects that are fairly similar or share properties, you may use interfaces or abstract classes. The Serializer component allows you to serialize and deserialize these objects using a "discriminator class mapping".

The discriminator is the field (in the serialized string) used to differentiate between the possible objects. In practice, when using the Serializer component, pass a ClassDiscriminatorResolverInterface implementation to the ObjectNormalizer.

The Serializer component provides an implementation of ClassDiscriminatorResolverInterface called ClassDiscriminatorFromClassMetadata which uses the class metadata factory and a mapping configuration to serialize and deserialize objects of the correct class.

When using this component inside a Symfony application and the class metadata factory is enabled as explained in the Attributes Groups section, this is already set up and you only need to provide the configuration. Otherwise:

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        // ...
use Symfony\Component\Serializer\Encoder\JsonEncoder;
use Symfony\Component\Serializer\Mapping\ClassDiscriminatorMapping;
use Symfony\Component\Serializer\Mapping\ClassDiscriminatorFromClassMetadata;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
use Symfony\Component\Serializer\Serializer;

$classMetadataFactory = new ClassMetadataFactory(new AnnotationLoader(new AnnotationReader()));

$discriminator = new ClassDiscriminatorFromClassMetadata($classMetadataFactory);

$serializer = new Serializer(
    [new ObjectNormalizer($classMetadataFactory, null, null, null, $discriminator)],
    ['json' => new JsonEncoder()]
);
    

Now configure your discriminator class mapping. Consider an application that defines an abstract CodeRepository class extended by GitHubCodeRepository and BitBucketCodeRepository classes:

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        namespace App;

use Symfony\Component\Serializer\Annotation\DiscriminatorMap;

/**
 * @DiscriminatorMap(typeProperty="type", mapping={
 *    "github"="App\GitHubCodeRepository",
 *    "bitbucket"="App\BitBucketCodeRepository"
 * })
 */
interface CodeRepository
{
    // ...
}
    

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        App\CodeRepository:
    discriminator_map:
        type_property: type
        mapping:
            github: 'App\GitHubCodeRepository'
            bitbucket: 'App\BitBucketCodeRepository'
    

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        <?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
        http://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
>
    <class name="App\CodeRepository">
        <discriminator-map type-property="type">
            <mapping type="github" class="App\GitHubCodeRepository" />
            <mapping type="bitbucket" class="App\BitBucketCodeRepository" />
        </discriminator-map>
    </class>
</serializer>
    

Once configured, the serializer uses the mapping to pick the correct class:

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        $serialized = $serializer->serialize(new GitHubCodeRepository());
// {"type": "github"}

$repository = $serializer->deserialize($serialized, CodeRepository::class, 'json');
// instanceof GitHubCodeRepository
    

Performance

To figure which normalizer (or denormalizer) must be used to handle an object, the Serializer class will call the supportsNormalization() (or supportsDenormalization()) of all registered normalizers (or denormalizers) in a loop.

The result of these methods can vary depending on the object to serialize, the format and the context. That's why the result is not cached by default and can result in a significant performance bottleneck.

However, most normalizers (and denormalizers) always return the same result when the object's type and the format are the same, so the result can be cached. To do so, make those normalizers (and denormalizers) implement the CacheableSupportsMethodInterface and return true when hasCacheableSupportsMethod() is called.

Note
All built-in normalizers and denormalizers as well the ones included in API Platform natively implement this interface.

Learn more

How to Use the Serializer

The Serializer Component

The Serializer Component

Installation

Usage

Serializing an Object

Deserializing an Object

Deserializing in an Existing Object

Attributes Groups

Selecting Specific Attributes

Ignoring Attributes

Converting Property Names when Serializing and Deserializing

CamelCase to snake_case

Serializing Boolean Attributes

Using Callbacks to Serialize Properties with Object Instances

Normalizers

Encoders

Built-in Encoders

The `JsonEncoder`

The `CsvEncoder`

The `XmlEncoder`

The `YamlEncoder`

Handling Circular References

Handling Serialization Depth

Handling Arrays

The `XmlEncoder`

Context

Handling Constructor Arguments

Recursive Denormalization and Type Safety

Serializing Interfaces and Abstract Classes

Performance

Learn more

What is Symfony?

Learn Symfony

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Community

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Services

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