Valinor • PHP object mapper with strong type support

Valinor is a PHP library that helps to map any input into a strongly-typed value object structure.

The conversion can handle native PHP types as well as other well-known advanced type annotations like array shapes, generics and more.

Why?

There are many benefits of using value objects instead of plain arrays and scalar values in a modern codebase, among which:

1. Data and behaviour encapsulation — locks an object's behaviour inside its class, preventing it from being scattered across the codebase.
2. Data validation — guarantees the valid state of an object.
3. Immutability — ensures the state of an object cannot be changed during runtime.

When mapping any source to an object structure, this library will ensure that all input values are properly converted to match the types of the nodes — class properties or method parameters. Any value that cannot be converted to the correct type will trigger an error and prevent the mapping from completing.

These checks guarantee that if the mapping succeeds, the object structure is perfectly valid, hence there is no need for further validation nor type conversion: the objects are ready to be used.

Static analysis

A strongly-typed codebase allows the usage of static analysis tools like PHPStan and Psalm that can identify issues in a codebase without running it.

Moreover, static analysis can help during a refactoring of a codebase with tools like an IDE or Rector.

Usage

Installation

composer require cuyz/valinor

Example

An application must handle the data coming from an external API; the response has a JSON format and describes a thread and its answers. The validity of this input is unsure, besides manipulating a raw JSON string is laborious and inefficient.

{
    "id": 1337,
    "content": "Do you like potatoes?",
    "date": "1957-07-23 13:37:42",
    "answers": [
        {
            "user": "Ella F.",
            "message": "I like potatoes",
            "date": "1957-07-31 15:28:12"
        },
        {
            "user": "Louis A.",
            "message": "And I like tomatoes",
            "date": "1957-08-13 09:05:24"
        }
    ]
}

The application must be certain that it can handle this data correctly; wrapping the input in a value object will help.

---

A schema representing the needed structure must be provided, using classes.

final class Thread
{
    public function __construct(
        public readonly int $id,
        public readonly string $content,
        public readonly DateTimeInterface $date,
        /** @var Answer[] */
        public readonly array $answers, 
    ) {}
}

final class Answer
{
    public function __construct(
        public readonly string $user,
        public readonly string $message,
        public readonly DateTimeInterface $date,
    ) {}
}

Then a mapper is used to hydrate a source into these objects.

public function getThread(int $id): Thread
{
    $rawJson = $this->client->request("https://example.com/thread/$id");

    try {   
        return (new \CuyZ\Valinor\MapperBuilder())
            ->mapper()
            ->map(
                Thread::class,
                new \CuyZ\Valinor\Mapper\Source\JsonSource($rawJson)
            );
    } catch (\CuyZ\Valinor\Mapper\MappingError $error) {
        // Do something…
    }
}

Mapping advanced types

Although it is recommended to map an input to a value object, in some cases mapping to another type can be easier/more flexible.

It is for instance possible to map to an array of objects:

try {
    $objects = (new \CuyZ\Valinor\MapperBuilder())
        ->mapper()
        ->map(
            'array<' . SomeClass::class . '>',
            [/* … */]
        );
} catch (\CuyZ\Valinor\Mapper\MappingError $error) {
    // Do something…
}

For simple use-cases, an array shape can be used:

try {
    $array = (new \CuyZ\Valinor\MapperBuilder())
        ->mapper()
        ->map(
            'array{foo: string, bar: int}',
            [/* … */]
        );
    
    echo $array['foo'];
    echo $array['bar'] * 2;
} catch (\CuyZ\Valinor\Mapper\MappingError $error) {
    // Do something…
}

Validation

The source given to a mapper can never be trusted, this is actually the very goal of this library: transforming an unstructured input to a well-defined object structure. If the mapper cannot guess how to cast a certain value, it means that it is not able to guarantee the validity of the desired object thus it will fail.

Any issue encountered during the mapping will add an error to an upstream exception of type \CuyZ\Valinor\Mapper\MappingError. It is therefore always recommended wrapping the mapping function call with a try/catch statement and handle the error properly.

More specific validation should be done in the constructor of the value object, by throwing an exception if something is wrong with the given data. A good practice would be to use lightweight validation tools like Webmozart Assert.

When the mapping fails, the exception gives access to the root node. This recursive object allows retrieving all needed information through the whole mapping tree: path, values, types and messages, including the issues that caused the exception.

final class SomeClass
{
    public function __construct(private string $someValue)
    {
        Assert::startsWith($someValue, 'foo_');
    }
}

try {
   (new \CuyZ\Valinor\MapperBuilder())
       ->mapper()
       ->map(
           SomeClass::class,
           ['someValue' => 'bar_baz']
       );
} catch (\CuyZ\Valinor\Mapper\MappingError $error) {
    $node = $error->node()->children()['someValue'];

    // Should print something similar to:
    // > Expected a value to start with "foo_". Got: "bar_baz"
    var_dump($node->messages()[0]);

    // The name of a node can be accessed 
    $name = $node->name();

    // The logical path of a node contains dot separated names of its parents
    $path = $node->path();
    
    // The type of the node can be cast to string to enhance suggestion messages 
    $type = (string)$node->type();

    // It is important to check if a node is valid before getting its value
    if ($node->isValid()) {
        // The processed value of the node can be different from original input
        $value = $node->value();
    }

    // All messages bound to the node can be accessed
    foreach ($node->messages() as $message) {
        // Errors can be retrieved by filtering like below:
        if ($message->isError()) {
            // Do something…
        }
    }

    // If the node is a branch, its children can be recursively accessed
    foreach ($node->children() as $child) {
        // Do something…  
    }
}

Source

Any source can be given to the mapper, but some helpers can be used for more convenience:

function map($source) {
    return (new \CuyZ\Valinor\MapperBuilder())
        ->mapper()
        ->map(SomeClass::class, $source);
}

map(new \CuyZ\Valinor\Mapper\Source\JsonSource($jsonString));

map(new \CuyZ\Valinor\Mapper\Source\YamlSource($yamlString));

// File containing valid Json or Yaml content and with valid extension
map(new \CuyZ\Valinor\Mapper\Source\FileSource(
    new SplFileObject('path/to/my/file.json')
));

Construction strategy

During the mapping, instances of the objects are created and hydrated with the correct values. Construction strategies will determine what values are needed and how an object is built.

An object can provide either…

• …a constructor that will be called with proper parameters.
• …a list of properties that will be filled with proper values — even if they are private.

Handled types

To prevent conflicts or duplication of the type annotations, this library tries to handle most of the type annotations that are accepted by PHPStan and Psalm.

Scalar

final class SomeClass
{
    public function __construct(
        private bool $boolean,

        private float $float,

        private int $integer,

        /** @var positive-int */
        private int $positiveInteger,

        /** @var negative-int */
        private int $negativeInteger,

        /** @var int<-42, 1337> */
        private int $integerRange,

        /** @var int<min, 0> */
        private int $integerRangeWithMinRange,

        /** @var int<0, max> */
        private int $integerRangeWithMaxRange,

        private string $string,
        
        /** @var non-empty-string */
        private string $nonEmptyString,

        /** @var class-string */
        private string $classString,

        /** @var class-string<SomeInterface> */
        private string $classStringOfAnInterface,
    ) {}
}

Object

final class SomeClass
{
    public function __construct(
        private SomeClass $class,

        private DateTimeInterface $interface,

        /** @var SomeInterface&AnotherInterface */
        private object $intersection,

        /** @var SomeCollection<SomeClass> */
        private SomeCollection $classWithGeneric,
    ) {}
}

/**
 * @template T of object 
 */
final class SomeCollection
{
    public function __construct(
        /** @var array<T> */
        private array $objects,
    ) {}
}

Array & lists

final class SomeClass
{
    public function __construct(
        /** @var string[] */
        private array $simpleArray,

        /** @var array<string> */
        private array $arrayOfStrings,

        /** @var array<string, SomeClass> */
        private array $arrayOfClassWithStringKeys,

        /** @var array<int, SomeClass> */
        private array $arrayOfClassWithIntegerKeys,

        /** @var non-empty-array<string> */
        private array $nonEmptyArrayOfStrings,

        /** @var non-empty-array<string, SomeClass> */
        private array $nonEmptyArrayWithStringKeys,
        
        /** @var list<string> */
        private array $listOfStrings,
        
        /** @var non-empty-list<string> */
        private array $nonEmptyListOfStrings,

        /** @var array{foo: string, bar: int} */
        private array $shapedArray,

        /** @var array{foo: string, bar?: int} */
        private array $shapedArrayWithOptionalElement,

        /** @var array{string, bar: int} */
        private array $shapedArrayWithUndefinedKey,
    ) {}
}

Union

final class SomeClass
{
    public function __construct(
        private int|string $simpleUnion,
        
        /** @var class-string<SomeInterface>|class-string<AnotherInterface> */
        private string $unionOfClassString,
        
        /** @var array<SomeInterface|AnotherInterface> */
        private array $unionInsideArray,
    ) {}
}

Static analysis

To help static analysis of a codebase using this library, an extension for PHPStan and a plugin for Psalm are provided. They enable these tools to better understand the behaviour of the mapper.

Considering at least one of those tools are installed on a project, below are examples of the kind of errors that would be reported.

Mapping to an array of classes

final class SomeClass
{
    public function __construct(
        public readonly string $foo,
        public readonly int $bar,
    ) {}
}

$objects = (new \CuyZ\Valinor\MapperBuilder())
    ->mapper()
    ->map(
        'array<' . SomeClass::class . '>',
        [/* … */]
    );

foreach ($objects as $object) {
    // ✅
    echo $object->foo;
    
    // ✅
    echo $object->bar * 2;
    
    // ❌ Cannot perform operation between `string` and `int`
    echo $object->foo * $object->bar;
    
    // ❌ Property `SomeClass::$fiz` is not defined
    echo $object->fiz;
} 

Mapping to a shaped array

$array = (new \CuyZ\Valinor\MapperBuilder())
    ->mapper()
    ->map(
        'array{foo: string, bar: int}',
        [/* … */]
    );

// ✅
echo $array['foo'];

// ❌ Expected `string` but got `int`
echo strtolower($array['bar']);

// ❌ Cannot perform operation between `string` and `int`
echo $array['foo'] * $array['bar'];

// ❌ Offset `fiz` does not exist on array
echo $array['fiz']; 

---

To activate this feature, the configuration must be updated for the installed tool(s):

PHPStan

includes:
    - vendor/cuyz/valinor/qa/PHPStan/valinor-phpstan-configuration.php

Psalm

<plugins>
    <plugin filename="vendor/cuyz/valinor/qa/Psalm/Plugin/TreeMapperPsalmPlugin.php"/>
</plugins>