PHP 數(shù)據(jù)映射器模式

目的

數(shù)據(jù)映射器是一個(gè)數(shù)據(jù)訪問(wèn)層，用于將數(shù)據(jù)在持久性數(shù)據(jù)存儲(chǔ)（通常是一個(gè)關(guān)系數(shù)據(jù)庫(kù)）和內(nèi)存中的數(shù)據(jù)表示（領(lǐng)域?qū)樱┲g進(jìn)行相互轉(zhuǎn)換。其目的是為了將數(shù)據(jù)的內(nèi)存表示、持久存儲(chǔ)、數(shù)據(jù)訪問(wèn)進(jìn)行分離。該層由一個(gè)或者多個(gè)映射器組成（或者數(shù)據(jù)訪問(wèn)對(duì)象），并且進(jìn)行數(shù)據(jù)的轉(zhuǎn)換。映射器的實(shí)現(xiàn)在范圍上有所不同。通用映射器將處理許多不同領(lǐng)域的實(shí)體類(lèi)型，而專(zhuān)用映射器將處理一個(gè)或幾個(gè)。

此模式的主要特點(diǎn)是，與Active Record不同，其數(shù)據(jù)模式遵循單一職責(zé)原則(Single Responsibility Principle)。

例子

• DB Object Relational Mapper (ORM) : Doctrine2 使用 DAO “EntityRepository” 作為DAO

UML 圖

代碼

User.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DataMapper;

class User
{
    public static function fromState(array $state): User
    {
        // validate state before accessing keys!

        return new self(
            $state['username'],
            $state['email']
        );
    }

    public function __construct(private string $username, private string $email)
    {
    }

    public function getUsername(): string
    {
        return $this->username;
    }

    public function getEmail(): string
    {
        return $this->email;
    }
}

UserMapper.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DataMapper;

use InvalidArgumentException;

class UserMapper
{
    public function __construct(private StorageAdapter $adapter)
    {
    }

    /**
     * finds a user from storage based on ID and returns a User object located
     * in memory. Normally this kind of logic will be implemented using the Repository pattern.
     * However the important part is in mapRowToUser() below, that will create a business object from the
     * data fetched from storage
     */
    public function findById(int $id): User
    {
        $result = $this->adapter->find($id);

        if ($result === null) {
            throw new InvalidArgumentException("User #$id not found");
        }

        return $this->mapRowToUser($result);
    }

    private function mapRowToUser(array $row): User
    {
        return User::fromState($row);
    }
}

StorageAdapter.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DataMapper;

class StorageAdapter
{
    public function __construct(private array $data)
    {
    }

    /**
     * @return array|null
     */
    public function find(int $id)
    {
        if (isset($this->data[$id])) {
            return $this->data[$id];
        }

        return null;
    }
}

測(cè)試

Tests/DataMapperTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DataMapper\Tests;

use InvalidArgumentException;
use DesignPatterns\Structural\DataMapper\StorageAdapter;
use DesignPatterns\Structural\DataMapper\User;
use DesignPatterns\Structural\DataMapper\UserMapper;
use PHPUnit\Framework\TestCase;

class DataMapperTest extends TestCase
{
    public function testCanMapUserFromStorage()
    {
        $storage = new StorageAdapter([1 => ['username' => 'domnikl', 'email' => 'liebler.dominik@gmail.com']]);
        $mapper = new UserMapper($storage);

        $user = $mapper->findById(1);

        $this->assertInstanceOf(User::class, $user);
    }

    public function testWillNotMapInvalidData()
    {
        $this->expectException(InvalidArgumentException::class);

        $storage = new StorageAdapter([]);
        $mapper = new UserMapper($storage);

        $mapper->findById(1);
    }
}