1. 设计模式
  2. 扩展模式
  3. 数据映射模式

数据映射模式

目的

数据映射器，是一个数据访问层，它在持久数据存储（通常是关系数据库）和内存数据（领域层）之间执行数据的双向传输。该模式的目标是使内存中的数据和持久层中的数据存储相互独立，并保持数据映射器本身的独立性。领域层由一个或多个映射器（或数据访问对象）组成，并执行数据传输。数据映射器的实现方式各不相同。通用映射器将处理许多不同领域的实体类型，专用映射器只处理一个或少量实体类型。

与活动记录（Active Record）模式不同，数据映射模式的关键点在于：数据模型遵循单一职责原则。

使用场景

  • 数据库对象关系映射（ORM）：Doctrine2 使用名为 EntityRepository 的 DAO

UML 类图

数据映射模式类图

代码

User.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DataMapper;

class User
{
    private string $username;
    private string $email;

    public static function fromState(array $state): User
    {
        // validate state before accessing keys!
        return new self(
            $state['username'],
            $state['email']
        );
    }

    public function __construct(string $username, string $email)
    {
        // validate parameters before setting them!
        $this->username = $username;
        $this->email = $email;
    }

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

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

UserMapper.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DataMapper;

use InvalidArgumentException;

class UserMapper
{
    private StorageAdapter $adapter;

    public function __construct(StorageAdapter $storage)
    {
        $this->adapter = $storage;
    }

    /**
     * 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

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DataMapper;

class StorageAdapter
{
    private array $data = [];

    public function __construct(array $data)
    {
        $this->data = $data;
    }

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

        return null;
    }
}

测试

Tests/DataMapperTest.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DataMapper\Tests;

use InvalidArgumentException;
use DesignPatterns\Extend\DataMapper\StorageAdapter;
use DesignPatterns\Extend\DataMapper\User;
use DesignPatterns\Extend\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);
    }
}
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