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Object Mapper

Installation

composer require league/object-mapper

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About

This library allows magic-less conversion from serialized data to object and back. Unlike other object mappers, this library does not rely on magic reflection to set private properties. It hydrates and serializes objects as if you would do it by hand. The hydration mechanism inspects the constructor and figures out which keys need to map to which properties. The serialization mechanism inspects all public properties and getter-methods, converts the values from objects to plain data-structures. Unlike "magic" hydration mechanisms, that are able to grab private properties, this way to map objects opens the door to object mapping without reflection. You get all the convenience with none of the guilt (or performance hits).

This is a utility that converts structured request data (for example: decoded JSON) into a complex object structure. The intended use of this utility is to receive request data and convert this into Command or Query object. The library is designed to follow a convention and does not validate input.

When and why would you use this?

That's a good question, so let's dig in. Initially, this library was created to map plain data (like JSON request bodies) to strict object structures. The use of object (DTOs, Query and Command objects) is a great way to create expressive code that is easy to understand. Objects can be trusted to correctly represent concepts in your domain. The downside of using these objects is that they can be tedious to use. Construction and serialization becomes repetitive and writing the same code over and over is boring. This library aims to remove the boring parts of object hydration and serialization.

This library was built with two specific use-cases in mind:

  1. Construction of DTOs, Query-object, and Command-objects.
  2. Serialization and hydration of Event-objects.

Object hydration and serialization can be achieved at zero expense, due to an ahead-of-time resolving steps using code generation.

Quick links:

Design goals

This package was created with a couple design goals in mind. They are the following:

  • Object creation should not be too magical (use no reflection for instantiation)
  • There should not be a hard runtime requirement on reflection
  • Constructed objects should be valid from construction
  • Construction through (static) named constructors should be supported

Usage

This library supports hydration and serialization of objects.

Hydration usage

By default, input is mapped by property name, and types need to match. By default, keys are mapped from snake_case input to camelCase properties. If you want to keep the key names you can use the KeyFormatterWithoutConversion.

use League\ObjectMapper\ObjectMapperUsingReflection;

$mapper = new ObjectMapperUsingReflection();

class ExampleCommand
{
    public function __construct(
        public readonly string $name,
        public readonly int $birthYear,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'name' => 'de Jonge',
        'birth_year' => 1987
    ],
);

$command->name === 'de Jonge';
$command->birthYear === 1987;

Complex objects are automagically resolved.

class ChildObject
{
    public function __construct(
        public readonly string $value,
    ) {}
}

class ParentObject
{
    public function __construct(
        public readonly string $value,
        public readonly ChildObject $child,
    ) {}
}

$command = $mapper->hydrateObject(
    ParentObject::class,
    [
        'value' => 'parent value',
        'child' => [
            'value' => 'child value',
        ]
    ],
);

A simple doc-comment ensures that arrays of objects are automagically converted.

class ChildObject
{
    public function __construct(
        public readonly string $value,
    ) {}
}

class ParentObject
{
    /**
     * @param ChildObject[] $list
     */
    public function __construct(
        public readonly array $list,
    ) {}
}

$object = $mapper->hydrateObject(ParentObject::class, [
  'list' => [
    ['value' => 'one'],
    ['value' => 'two'],
  ],
]);

$object->list[0]->value === 'one';
$object->list[1]->value === 'two';

The library supports the following formats:

  • @param Type[] $name
  • @param array<Type> $name
  • @param array<string, Type> $name
  • @param array<int, Type> $name

Custom mapping key

use League\ObjectMapper\MapFrom;

class ExampleCommand
{
    public function __construct(
        public readonly string $name,
        #[MapFrom('year')]
        public readonly int $birthYear,
    ) {}
}

Mapping from multiple keys

You can pass an array to capture input from multiple input keys. This is useful when multiple values represent a singular code concept. The array allows you to rename keys as well, further decoupling the input from the constructed object graph.

use League\ObjectMapper\MapFrom;

class BirthDate
{
    public function __construct(
        public int $year,
        public int $month,
        public int $day
    ){}
}

class ExampleCommand
{
    public function __construct(
        public readonly string $name,
        #[MapFrom(['year_of_birth' => 'year', 'month', 'day'])]
        public readonly BirthDate $birthDate,
    ) {}
}

$mapper->hydrateObject(ExampleCommand::class, [
    'name' => 'Frank',
    'year_of_birth' => 1987,
    'month' => 11,
    'day' => 24,
]);

Property casting

When the input type and property types are not compatible, values can be cast to specific scalar types.

Casting to scalar values

use League\ObjectMapper\PropertyCasters\CastToType;

class ExampleCommand
{
    public function __construct(
        #[CastToType('integer')]
        public readonly int $number,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'number' => '1234',
    ],
);

Casting to a list of scalar values

use League\ObjectMapper\PropertyCasters\CastListToType;

class ExampleCommand
{
    public function __construct(
        #[CastListToType('integer')]
        public readonly array $numbers,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'numbers' => ['1234', '2345'],
    ],
);

Casting to a list of objects

use League\ObjectMapper\PropertyCasters\CastListToType;

class Member
{
    public function __construct(
        public readonly string $name,
    ) {}
}

class ExampleCommand
{
    public function __construct(
        #[CastListToType(Member::class)]
        public readonly array $members,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'members' => [
            ['name' => 'Frank'],
            ['name' => 'Renske'],
        ],
    ],
);

Casting to DateTimeImmutable objects

use League\ObjectMapper\PropertyCasters\CastToDateTimeImmutable;

class ExampleCommand
{
    public function __construct(
        #[CastToDateTimeImmutable('!Y-m-d')]
        public readonly DateTimeImmutable $birthDate,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'birthDate' => '1987-11-24',
    ],
);

Casting to Uuid objects (ramsey/uuid)

use League\ObjectMapper\PropertyCasters\CastToUuid;
use Ramsey\Uuid\UuidInterface;

class ExampleCommand
{
    public function __construct(
        #[CastToUuid]
        public readonly UuidInterface $id,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'id' => '9f960d77-7c9b-4bfd-9fc4-62d141efc7e5',
    ],
);

Using multiple casters per property

Create rich compositions of casting by using multiple casters.

use League\ObjectMapper\PropertyCasters\CastToArrayWithKey;
use League\ObjectMapper\PropertyCasters\CastToType;
use League\ObjectMapper\MapFrom;
use Ramsey\Uuid\UuidInterface;

class ExampleCommand
{
    public function __construct(
        #[CastToType('string')]
        #[CastToArrayWithKey('nested')]
        #[MapFrom('number')]
        public readonly array $stringNumbers,
    ) {}
}

$command = $mapper->hydrateObject(
    ExampleCommand::class,
    [
        'number' => [1234],
    ],
);

$command->stringNumbers === ['nested' => [1234]];

Creating your own property casters

You can create your own property caster to handle complex cases that cannot follow the default conventions. Common cases for casters are union types or intersection types.

Property casters give you full control over how a property is constructed. Property casters are attached to properties using attributes, in fact, they are attributes.

Let's look at an example of a property caster:

use Attribute;
use League\ObjectMapper\ObjectMapper;
use League\ObjectMapper\PropertyCaster;

#[Attribute(Attribute::TARGET_PARAMETER)]
class CastToMoney implements PropertyCaster
{
    public function __construct(
        private string $currency
    ) {}

    public function cast(mixed $value, ObjectMapper $mapper) : mixed
    {
        return new Money($value, Currency::fromString($this->currency));
    }
}

// ----------------------------------------------------------------------

#[Attribute(Attribute::TARGET_PARAMETER)]
class CastUnionToType implements PropertyCaster
{
    public function __construct(
        private array $typeToClassMap
    ) {}

    public function cast(mixed $value, ObjectMapper $mapper) : mixed
    {
        assert(is_array($value));

        $type = $value['type'] ?? 'unknown';
        unset($value['type']);
        $className = $this->typeToClassMap[$type] ?? null;

        if ($className === null) {
            throw new LogicException("Unable to map type '$type' to class.");
        }

        return $mapper->hydrateObject($className, $value);
    }
}

You can now use these as attributes on the object you wish to hydrate:

class ExampleCommand
{
    public function __construct(
        #[CastToMoney('EUR')]
        public readonly Money $money,
        #[CastUnionToType(['some' => SomeObject::class, 'other' => OtherObject::class])]
        public readonly SomeObject|OtherObject $money,
    ) {}
}

Static constructors

Objects that require construction through static construction are supported. Mark the static method using the Constructor attribute. In these cases, the attributes should be placed on the parameters of the static constructor, not on __construct.

use League\ObjectMapper\Constructor;
use League\ObjectMapper\MapFrom;

class ExampleCommand
{
    private function __construct(
        public readonly string $value,
    ) {}

    #[Constructor]
    public static function create(
        #[MapFrom('some_value')]
        string $value
    ): static {
        return new static($value);
    }
}

Key formatters

By default, keys are converted from snake_case input to camelCase properties. However, you can control how keys are mapped by passing a key formatter to the DefinitionProvider that is handed to the object mapper constructor:

use League\ObjectMapper\DefinitionProvider;
use League\ObjectMapper\KeyFormatterWithoutConversion;
use League\ObjectMapper\ObjectMapperUsingReflection;

$mapper = new ObjectMapperUsingReflection(
    new DefinitionProvider(
        keyFormatter: new KeyFormatterWithoutConversion(),
    ),
);

This library ships with a KeyFormatterWithoutConversion that can be used if no conversion is desired. You can implement the KeyFormatter interface if you need custom conversion logic.

Serialization usage

By default, this library maps the public properties and getters to snake_cased arrays with plain data. When user-defined objects are encountered, these are automatically converted to the plain data counterpart.

class ExampleCommand
{
    public function __construct(
        public readonly string $name,
        public readonly int $birthYear,
    ) {}
}


$command = new ExampleCommand('de Jonge', 1987);
$payload = $mapper->serializeObject($command);

$payload['name'] === 'de Jonge';
$payload['birth_year'] === 1987;

Custom key mapping

Serialization inverts the key mapping used by hydration in a symmetrical way, including the mapping from multiple keys.

use League\ObjectMapper\MapFrom;

class BirthDate
{
    public function __construct(
        public int $year,
        public int $month,
        public int $day
    ){}
}

class ExampleCommand
{
    public function __construct(
        #[MapFrom('my_name')]
        public readonly string $name,
        #[MapFrom(['year_of_birth' => 'year', 'month', 'day'])]
        public readonly BirthDate $birthDate,
    ) {}
}

$command = new ExampleCommand(
  'de Jonge',
  new BirthDate(1987, 11, 24)
);

$payload = $mapper->serializeObject($command);

$payload['my_name'] === 'de Jonge';
$payload['year_of_birth'] === 1987;
$payload['month'] === 11;
$payload['day'] === 24;

Property serialization

Similar to casters, custom serialization logic can be added by using "property serializers". Property serialization are custom annotations that provide a hook into the serialization process, allowing you to gain full control over the serialization mechanism whenever you need it.

use League\ObjectMapper\ObjectMapper;
use League\ObjectMapper\PropertySerializer;

#[Attribute(Attribute::TARGET_PARAMETER | Attribute::TARGET_METHOD | Attribute::TARGET_PROPERTY)]
class UppercaseString implements PropertySerializer
{
    public function serialize(mixed $value, ObjectMapper $mapper): string
    {
        assert(is_string($value));
        
        return strtoupper($value);
    }
}

class Shout
{
    public function __construct(
        private readonly string $message
    ) {}
    
    #[UppercaseString]
    public function what(): string
    {
        return $this->message();
    }
}

$payload = $mapper->serializeObject(new Shout('Hello, World!');

$payload['what'] === 'HELLO, WORLD!';

Symmetrical conversion

If configured consistently, hydration and serialization can be used to translate an object to raw data and back to the original object. A class can implement both the PropertyCasterandPropertySerializer` interface to become a symmetrical conversion mechanism.

An example of this is the implementation of CastToArrayWithKey:

use League\ObjectMapper\ObjectMapper;
use League\ObjectMapper\PropertyCaster;
use League\ObjectMapper\PropertySerializer;

class CastToArrayWithKey implements PropertyCaster, PropertySerializer
{
    public function __construct(private string $key)
    {
    }

    public function cast(mixed $value, ObjectMapper $mapper): mixed
    {
        return [$this->key => $value];
    }

    public function serialize(mixed $value, ObjectMapper $mapper): mixed
    {
        if (is_object($value)) {
            $value = $hydrator->serializeObject($value);
        }

        return $value[$this->key] ?? null;
    }
}

It's important to know that serialization and hydration hooks are triggered before any default conversion happens. If you wish to operate on serialized or hydrated data, you can hydrate/serialize the inner data/objects.

⚠️ Caster and serializer order

In order to make hydration and serialization symmetrical (allowing back and forth conversion), the order of serializers called is reversed for promoted properties.

Omitting data for serialization

Data can be omitted from serialization. By default, all public methods and properties are included for serialization. There are two ways to exclude data, both methods use attributes.

The MapperSettings attribute can be specified at class-level to exclude either all public properties, public methods, or both (the last being rather useless, of course).

use League\ObjectMapper\MapperSettings;

#[MapperSettings(serializePublicMethods: false)]
class ClassThatDoesNotSerializePublicMethods
{
    // class body
}

#[MapperSettings(serializePublicProperties: false)]
class ClassThatDoesNotSerializePublicProperties
{
    // class body
}

The MapperSettings attribute can also be specified on interfaces that are implemented by classes. In this case, the first available MapperSettings will be used.

use League\ObjectMapper\MapperSettings;

#[MapperSettings(serializePublicMethods: false)]
interface InterfaceThatDoesNotSerializePublicMethods
{
    public function resource(): string;
}

class ClassThatInheritsMapperSettingsFromInterface implements InterfaceThatDoesNotSerializePublicMethods
{
    public function resource(): string
    {
        return 'foo';
    }
}

⚠️ Note that MapperSettings defined on parent classes will not be used, to prevent confusion and ensure consistent performance with class inheritance.

Alternatively, specific methods and properties can be excluded from serialization by using the DoNotSerialize attribute.

use League\ObjectMapper\DoNotSerialize;

class ClassThatExcludesCertainDataPoints
{
    public function __construct(
        public string $includedProperty,
        #[DoNotSerialize]
        public string $excludedProperty,
    ) {}
    
    public function includedMethod(): string
    {
        return 'included';
    }
    
    #[DoNotSerialize]
    public function excludedMethod(): string
    {
        return 'excluded';
    }
}

Maximizing performance

Reflection and dynamic code paths can be a performance issue in the hot-path. To remove the expense, an optimized implementation can be generated. The generated PHP code performs the same hydration and serialization of classes as the reflection-based implementation would. It's sort of a pre-compiler for this logic.

You can generate a fully optimized mapper for a known set of classes. The generator will produce the code required for constructing the entire object tree, automatically resolving the nested proprties it must map.

The dumped code is 3-10x faster than the reflection based implementation.

use League\ObjectMapper\ObjectMapper;
use League\ObjectMapper\ObjectMapperCodeGenerator;

$dumpedClassNamed = "AcmeCorp\\YourOptimizedMapper";
$dumper = new ObjectMapperCodeGenerator();
$classesToDump = [SomeCommand::class, AnotherCommand::class];

$code = $dumper->dump($classesToDump, $dumpedClassNamed);
file_put_contents('src/AcmeCorp/YourOptimizedMapper.php', $code);

/** @var ObjectMapper $mapper */
$mapper = new AcmeCorp\YourOptimizedMapper();
$someObject = $mapper->hydrateObject(SomeObject::class, $payload);

Tip: Use league/construct-finder

You can use the construct finder package from The PHP League to find all classes in a given directory.

composer require league/construct-finder
$classesToDump = ConstructFinder::locatedIn($directoryName)->findClassNames();

Alternatives

This package is not unique, there are a couple implementations our there that do the same, similar, or more than this package does.

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