README

A lightweight, explicit, type-safe PHP 8.3 library for hydrating PHP objects from database rows, without requiring an ORM, annotations, attributes, or complex metadata systems.

This library is ideal for applications that:

• Prefer writing SQL rather than generating it
• Use DTOs or readonly value objects
• Want predictable hydration without magical reflection
• Require nested object hydration from JOINed queries
• Want a small, focused library instead of an entire ORM layer

Designed to be framework-agnostic and extremely fast.

Features

• Simple, explicit mappings (no annotations or attributes)
• Hydrator for mapping flat SQL rows to DTOs
• EmbeddedObject for nested hydration (JOIN results)
• DbResults to hydrate directly from a PDOStatement iterator
• IndexedDbResults for key-indexed hydration (e.g., $users[$id])
• Zero dependencies
• No reflection
• Supports custom value objects, fromString(), and callables
• Automatic JSON decoding
• Strict error handling for mismatched schemas

Installation

composer require greenbean/db-hydration

Requires PHP 8.3+.

Basic Usage

1. Define a DTO

final readonly class UserDto
{
    public function __construct(
        public UserId $id,
        public string $email,
        public DateTimeImmutable $createdAt,
    ) {}
}

2. Define a mapping

use Greenbean\DbHydration\HydrationMapping;

final class UserMapping implements HydrationMapping
{
    public static function map(): array
    {
        return [
            'id'         => UserId::class,
            'email'      => 'string',
            'created_at' => DateTimeImmutable::class,
        ];
    }
}

3. Hydrate rows with the Hydrator

$hydrator = Hydrator::fromMapping(new UserMapping());

$rows = $pdo->query('SELECT id, email, created_at FROM users')
            ->fetchAll(PDO::FETCH_ASSOC);

$users = $hydrator->hydrateRows(UserDto::class, $rows);

Nested Hydration with JOINs

DTOs:

final readonly class ProfileDto
{
    public function __construct(
        public string $bio,
        public int $age,
    ) {}
}

final readonly class UserWithProfileDto
{
    public function __construct(
        public UserId $id,
        public string $email,
        public ProfileDto $profile,
    ) {}
}

Mapping:

final class ProfileMapping implements HydrationMapping
{
    public static function map(): array
    {
        return [
            'bio' => 'string',
            'age' => 'int',
        ];
    }
}

Create hydrators:

$profileHydrator = Hydrator::fromMapping(new ProfileMapping(), 'profile');

$userHydrator = Hydrator::fromMapping(
    new UserMapping(),
    prefix: 'u',
    injected: [],
    new EmbeddedObject(
        name: 'profile',
        prefix: 'profile',
        dtoClass: ProfileDto::class,
        hydrator: $profileHydrator
    )
);

SQL example:

SELECT
    u.id              AS u_id,
    u.email           AS u_email,
    p.bio             AS profile_bio,
    p.age             AS profile_age
FROM users u
LEFT JOIN profiles p ON p.user_id = u.id;

Hydrate:

$users = $userHydrator->hydrateRows(UserWithProfileDto::class, $rows);

Streaming Hydration

DbResults

$stmt = $pdo->query('SELECT id, email, created_at FROM users');

$results = new DbResults($hydrator, UserDto::class, $stmt);

foreach ($results as $user) {
    // $user is UserDto
}

IndexedDbResults

$stmt = $pdo->query('SELECT id, email, created_at FROM users');

$results = new IndexedDbResults('id', $hydrator, UserDto::class, $stmt);

foreach ($results as $id => $user) {
    // keyed by ID
}

Mapping Rules

Type	Meaning
int	Cast to integer
string	Cast to string
bool	Cast to boolean
json	Decode JSON into associative array
ClassName	Uses fromString() or constructor
callable	Developer-defined custom mapper

Error Handling

The hydrator throws exceptions for:

• Missing required columns
• Missing embedded columns
• Unrecognized mapping types
• Type conversion failures

Failures are explicit and loud, to catch mistakes early.

Requirements

• PHP 8.3+
• PDO
• Composer

License

MIT License.

Contributing

Pull requests are welcome. Please include:

• A clear summary of the change
• Tests where applicable
• Real-world examples when adding new features