The Serializer Component

Warning: You are browsing the documentation for Symfony 2.x, which is no longer maintained.

Read the updated version of this page for Symfony 7.3 (the current stable version).

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 simple 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

See also

This article explains how to use the Serializer features as an independent component in any PHP application. Read the How to Use the Serializer article to learn about how to use it in Symfony applications.

Using the Serializer component is really simple. You just need to set up the Serializer specifying which encoders and normalizer are going to be available:

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

$encoders = array(new XmlEncoder(), new JsonEncoder());
$normalizers = array(new ObjectNormalizer());

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

The preferred normalizer is the ObjectNormalizer, but other normalizers are available. All the examples shown below use the ObjectNormalizer.

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:

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

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', array('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

2.7

The support of serialization and deserialization groups was introduced in Symfony 2.7.

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.yml'));

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;
    }

    // ...
}

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);
$serializer = new Serializer(array($normalizer));

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

$obj2 = $serializer->denormalize(
    array('foo' => 'foo', 'bar' => 'bar'),
    'MyObj',
    null,
    array('groups' => array('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;

Ignoring Attributes

Note

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

2.3

The setIgnoredAttributes() method was introduced in Symfony 2.3.

2.7

Prior to Symfony 2.7, attributes were only ignored while serializing. Since Symfony 2.7, they are ignored when deserializing too.

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(array('age'));
$encoder = new JsonEncoder();

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

Converting Property Names when Serializing and Deserializing

2.7

The NameConverterInterface interface was introduced in Symfony 2.7.

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);

$serializer = new Serializer(array($normalizer), array(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

2.7

The CamelCaseToSnakeCaseNameConverter interface was introduced in Symfony 2.7.

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(array('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(array('createdAt' => $callback));

$serializer = new Serializer(array($normalizer), array($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 when using the Symfony Standard Edition with the serializer 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. It supports calling the constructor during the denormalization process.

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

.. versionadded:: 2.7
The ObjectNormalizer class was introduced in Symfony 2.7.

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');
$organization->setMembers(array($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();
});

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

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);

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

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

2.8

The ArrayDenormalizer class was introduced in 2.8. Prior to Symfony 2.8, only the serialization of arrays is supported.

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(
    array(new GetSetMethodNormalizer(), new ArrayDenormalizer()),
    array(new JsonEncoder())
);

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

Learn more

See also

A popular alternative to the Symfony Serializer Component is the third-party library, JMS serializer (versions before `v1.12.0` were released under the Apache license, so incompatible with GPLv2 projects).

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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