数据映射模式(Data Mapper)

由 学院君 创建于5年前, 最后更新于 8个月前

版本号 #3

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1、模式定义

在了解数据映射模式之前，先了解下数据映射，它是在持久化数据存储层(通常是关系型数据库)和驻于内存的数据表现层之间进行双向数据传输的数据访问层。

数据映射模式的目的是让持久化数据存储层、驻于内存的数据表现层、以及数据映射本身三者相互独立、互不依赖。这个数据访问层由一个或多个映射器(或者数据访问对象)组成，用于实现数据传输。通用的数据访问层可以处理不同的实体类型，而专用的则处理一个或几个。

数据映射模式的核心在于它的数据模型遵循单一职责原则(Single Responsibility Principle), 这也是和 Active Record 模式的不同之处。最典型的数据映射模式例子就是数据库 ORM 模型 (Object Relational Mapper)。

注：更多关于 Data Mapper 与 Active Record 的区别与联系请查看这篇文章了解更多 —— https://laravelacademy.org/post/966.html

准确来说该模式是个架构模式。

2、UML类图

3、示例代码

User.php

namespace DesignPatterns\Structural\DataMapper;

/**

*

* 这是数据库记录在内存的表现层

*

* 验证也在该对象中进行

*

*/

class User

{

/**

* @var int

*/

protected $userId;

/**

* @var string

*/

protected $username;

/**

* @var string

*/

protected $email;

/**

* @param null $id

* @param null $username

* @param null $email

*/

public function __construct($id = null, $username = null, $email = null)

{

$this->userId = $id;

$this->username = $username;

$this->email = $email;

}

/**

* @return int

*/

public function getUserId()

{

return $this->userId;

}

/**

* @param int $userId

*/

public function setUserID($userId)

{

$this->userId = $userId;

}

/**

* @return string

*/

public function getUsername()

{

return $this->username;

}

/**

* @param string $username

*/

public function setUsername($username)

{

$this->username = $username;

}

/**

* @return string

*/

public function getEmail()

{

return $this->email;

}

/**

* @param string $email

*/

public function setEmail($email)

{

$this->email = $email;

}

}

UserMapper.php

namespace DesignPatterns\Structural\DataMapper;

/**

* UserMapper类(数据映射类)

*/

class UserMapper

{

/**

* @var DBAL

*/

protected $adapter;

/**

* @param DBAL $dbLayer

*/

public function __construct(DBAL $dbLayer)

{

$this->adapter = $dbLayer;

}

/**

* 将用户对象保存到数据库

*

* @param User $user

*

* @return boolean

*/

public function save(User $user)

{

/* $data的键名对应数据库表字段 */

$data = array(

'userid' => $user->getUserId(),

'username' => $user->getUsername(),

'email' => $user->getEmail(),

);

/* 如果没有指定ID则在数据库中创建新纪录，否则更新已有记录 */

if (null === ($id = $user->getUserId())) {

unset($data['userid']);

$this->adapter->insert($data);

return true;

} else {

$this->adapter->update($data, array('userid = ?' => $id));

return true;

}

}

/**

* 基于ID在数据库中查找用户并返回用户实例

*

* @param int $id

*

* @throws \InvalidArgumentException

* @return User

*/

public function findById($id)

{

$result = $this->adapter->find($id);

if (0 == count($result)) {

throw new \InvalidArgumentException("User #$id not found");

}

$row = $result->current();

return $this->mapObject($row);

}

/**

* 获取数据库所有记录并返回用户实例数组

*

* @return array

*/

public function findAll()

{

$resultSet = $this->adapter->findAll();

$entries = array();

foreach ($resultSet as $row) {

$entries[] = $this->mapObject($row);

}

return $entries;

}

/**

* 映射表记录到对象

*

* @param array $row

*

* @return User

*/

protected function mapObject(array $row)

{

$entry = new User();

$entry->setUserID($row['userid']);

$entry->setUsername($row['username']);

$entry->setEmail($row['email']);

return $entry;

}

}

4、测试代码

Tests/DataMapperTest.php

namespace DesignPatterns\Structural\DataMapper\Tests;

use DesignPatterns\Structural\DataMapper\UserMapper;

use DesignPatterns\Structural\DataMapper\User;

/**

* UserMapperTest用于测试数据映射模式

*/

class DataMapperTest extends \PHPUnit_Framework_TestCase

{

/**

* @var UserMapper

*/

protected $mapper;

/**

* @var DBAL

*/

protected $dbal;

protected function setUp()

{

$this->dbal = $this->getMockBuilder('DesignPatterns\Structural\DataMapper\DBAL')

->disableAutoload()

->setMethods(array('insert', 'update', 'find', 'findAll'))

->getMock();

$this->mapper = new UserMapper($this->dbal);

}

public function getNewUser()

{

return array(array(new User(null, 'Odysseus', 'Odysseus@ithaca.gr')));

}

public function getExistingUser()

{

return array(array(new User(1, 'Odysseus', 'Odysseus@ithaca.gr')));

}

/**

* @dataProvider getNewUser

*/

public function testPersistNew(User $user)

{

$this->dbal->expects($this->once())

->method('insert');

$this->mapper->save($user);

}

/**

* @dataProvider getExistingUser

*/

public function testPersistExisting(User $user)

{

$this->dbal->expects($this->once())

->method('update');

$this->mapper->save($user);

}

/**

* @dataProvider getExistingUser

*/

public function testRestoreOne(User $existing)

{

$row = array(

'userid' => 1,

'username' => 'Odysseus',

'email' => 'Odysseus@ithaca.gr'

);

$rows = new \ArrayIterator(array($row));

$this->dbal->expects($this->once())

->method('find')

->with(1)

->will($this->returnValue($rows));

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

$this->assertEquals($existing, $user);

}

/**

* @dataProvider getExistingUser

*/

public function testRestoreMulti(User $existing)

{

$rows = array(array('userid' => 1, 'username' => 'Odysseus', 'email' => 'Odysseus@ithaca.gr'));

$this->dbal->expects($this->once())

->method('findAll')

->will($this->returnValue($rows));

$user = $this->mapper->findAll();

$this->assertEquals(array($existing), $user);

}

/**

* @expectedException \InvalidArgumentException

* @expectedExceptionMessage User #404 not found

*/

public function testNotFound()

{

$this->dbal->expects($this->once())

->method('find')

->with(404)

->will($this->returnValue(array()));

$user = $this->mapper->findById(404);

}

}