Database Design Patterns
May 24, 2015
This session introduces most well known design patterns to build PHP classes and objects that need to store and fetch data from a relational databases. The session will describe the difference between of the Active Record, the Table and Row Data Gateway and the Data Mapper pattern. We will also examine some technical advantages and drawbacks of these implementations. This talk will expose some of the best PHP tools, which ease database interactions and are built on top of these patterns.
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Enterprise Database Design Patterns in PHP
Hugo Hamon – OSIDays 2011
By Martin Fowler § Table Module § Transaction Script § Row Data Gateway § Table Data Gateway § Active Record § Data Mapper § Unit of Work § Identity Map § Data Transfer Object § …
Table Data Gateway
« An object that acts as a Gateway to
a database table. One instance
handles all the rows in the table. » Martin Fowler
Same as Data Access Object
Martin Fowler
CRUD
$table = new OrderGateway(new Connection('...'));
$table->insert('XX123456789', 358.80, 'unpaid');
$table->update(42, 'XX123456789', 358.80, 'paid');
$table->delete(42);
class OrderGateway
{
private $conn;
public function __construct(Connection $conn)
{
$this->conn = $conn;
}
}
class OrderGateway
{
public function insert($reference, $amount, $status)
{
$query = 'INSERT INTO orders (reference, amount, status) VALUES (?, ?, ?)';
$data = array($reference, $amount, $status);
$this->conn->executeQuery($query, $data);
return $this->conn->lastInsertId();
}
}
class OrderGateway
{
public function update($pk, $ref, $amount, $status)
{
$query = 'UPDATE orders SET reference = ?, amount = ?, status = ? WHERE id = ?';
$data = array($ref, $amount, $status, $pk);
return $this->conn->executeQuery($query, $data);
}
}
class OrderGateway
{
public function delete($pk)
{
return $this->conn->executeQuery(
'DELETE FROM orders WHERE id = ?',
array($pk)
);
}
}
Finders
$orders = $table->findAll();
$orders = $table->findPaidOrders();
$orders = $table->findUnpaidOrders();
$orders = $table->findBy(array(
'status' => 'paid',
'amount' => 250.00
));
$order = $table->find(42);
$order = $table->findOneBy(array('reference' => '...'));
class OrderGateway
{
public function findAll()
{
$query = 'SELECT * FROM orders';
return $this->conn->fetchAll($query);
}
public function find($pk)
{
$rs = $this->conn->findBy(array('id' => $pk));
return 1 === count($rs) ? $rs[0] : false;
}
}
public function findBy(array $criteria)
{
$where = array();
foreach ($criteria as $field => $value) {
$where[] = sprintf('%s = ?');
}
$q = sprintf(
'SELECT * FROM orders WHERE %s',
implode(' AND ', $where)
);
return $this->conn->fetchAll($q, array_values($criteria));
}
public function findPaidOrders()
{
return $this->findBy(array('status' => 'paid'));
}
public function findUnpaidOrders()
{
return $this->findBy(array('status' => 'unpaid'));
}
When to use it?
Row Data Gateway
« An object that acts as a Gateway to
a single record in a data source. There
is one instance per row. » Martin Fowler
CRUD
class Order
{
private $id;
private $reference;
private $amount;
private $vat;
private $total;
private $createdAt;
// Getters and setters for each property
// ...
}
$conn = new Connection('...');
$order = new OrderGateway();
$order->setReference('XX12345678');
$order->setAmount(300.00);
$order->setVat(58.80);
$order->setTotal(358.80);
$order->setCreatedAt(new DateTime());
$order->insert($conn);
class OrderGateway
{
public function insert(Connection $conn)
{
$query = 'INSERT INTO orders (reference, amount, vat, total, created_at) VALUES (?, ?, ?, ?, ?)';
$data = array(
$this->reference, $this->amount, $this->vat,
$this->total, $this->createdAt->format('Y-m-d H:i:s')
);
$conn->executeQuery($query, $data);
$this->id = $conn->lastInsertId();
}
}
Finders
OrderFinder::setConnection($conn);
$order = OrderFinder::findByReference('XX12345678');
echo sprintf('%01.2f euros', $order->getTotal());
class OrderFinder
{
static public function findByReference($reference)
{
$query = 'SELECT * FROM orders WHERE reference = ?';
$rs = static::getConnection()
->fetchSingle($query, array($reference))
;
return $rs ? OrderGateway::load($rs) : false;
}
}
class OrderGateway
{
static public function load(array $rs)
{
$order = new OrderGateway($rs['id']);
$order->setReference($rs['reference']);
$order->setAmount($rs['amount']);
$order->setVat($rs['vat']);
$order->setTotal($rs['total']);
$order->setCreatedAt(new DateTime($rs['created_at']));
return $order;
}
}
OrderFinder::setConnection($conn);
$orders = OrderFinder::findMostExpensiveOrders(10);
foreach ($orders as $order) {
echo $order->getReference(), "\n";
echo sprintf('%01.2f euros', $order->getTotal()), "\n";
echo "\n-----\n";
}
class OrderFinder
{
static public function findMostExpensiveOrders($limit)
{
$orders = array();
$query = 'SELECT * FROM orders ORDER BY total DESC LIMIT ?';
$rs = static::getConnection()->fetchAll($query, array($limit));
foreach ($rs as $data) {
$orders[] = OrderGateway::load($data);
}
return $orders;
}
}
When to use it?
Active Record
« An object that wraps a row in a
database table or view, encapsulates
the database access, and adds
domain logic on that data. » Martin Fowler
Active Record =
Row Data Gateway + Business Logic
Active Record =
Data + Behaviors
Active Record =
Properties + Methods
class Order
{
private $id;
private $reference;
private $amount;
private $vat;
private $vatRate;
private $total;
private $createdAt;
private $status;
private $isPaid;
// Getters and setters for each property
// ...
}
class Order
{
public function __construct($id = null)
{
if (null !== $id) {
$this->id = $id;
}
$this->vatRate = 0.00;
$this->vat = 0.00;
$this->amount = 0.00;
$this->total = 0.00;
$this->isPaid = false;
$this->status = 'processing';
$this->createdAt = new DateTime();
}
}
$conn = new Connection('...'); $order = new Order(); $order->setReference('XX12345678'); $order->setAmount(300.00); $order->setVatRate(0.196); $order->applyDiscount(20.00); $order->updateTotal(); $order->save($conn);
class Order { public function applyDiscount($discount) { $this->amount -= $discount; } public function updateTotal() { if ($this->vatRate) { $this->vat = $this->amount * $this->vatRate; } $this->total = $this->amount + $this->vat; } }
class Order
{
public function isPaid()
{
return $this->isPaid;
}
public function setPaid()
{
$this->isPaid = true;
}
}
class Order
{
public function isReadyForShipment()
{
return $this->isPaid() && 'complete' == $this->status;
}
public function ship($address)
{
$this->doShipment($address);
$this->status = 'shipped';
}
}
class OrderController
{
public function confirmAction($reference)
{
$conn = $this->getDatabaseConnection();
$order = ...;
$order->setPaid();
$order->save($conn);
if ($order->isReadyForShipment()) {
$order->ship();
return $this->view->render('ship.php', array('order' => $order));
}
return $this->view->render('pending.php', array('order' => $order));
}
}
Refactoring
abstract class ActiveRecord
{
protected $fields = array();
abstract public function getTableName();
public function save(Connection $conn)
{
// insert or update $fields in the database
}
public function delete(Connection $conn)
{
// delete the object from the database
}
}
class Order extends ActiveRecord
{
private $amount;
abstract public function getTableName()
{
return 'tbl_orders';
}
public function setAmount($amount)
{
$this->amount = $amount;
$this->fields['amount'] = $amount;
}
}
When to use it?
Data Mapper
« A layer of Mappers that moves data
between objects and a database
while keeping them independent of
each other and the mapper itself. » Martin Fowler
« Man in the Middle »
http://martinfowler.com
class OrderMapper
{
private $conn;
public function __construct(Connection $conn) {
$this->conn = $conn;
}
public function store(Order $order) {
// Execute the query to persist the object to the DB
}
public function remove(Order $order) {
// Executes the query to remove the object to the DB
}
}
$order = new Order();
$order->setReference('XX12345678');
$order->setAmount(300.00);
$order->setVatRate(0.196);
$order->updateTotal();
$conn = new Connection('mysql:host=localhost ...');
$mapper = new OrderMapper($conn);
$mapper->store($order);
class OrderMapper
{
public function findAll()
{
$objects = array();
$query = 'SELECT id, reference, vat ... FROM orders';
foreach ($this->conn->fetchAll($query) as $data) {
$object = new Order($data['id']);
$object->load($data);
$objects[] = $object;
}
return $objects;
}
}
class OrderMapper
{
public function find($pk)
{
$query = 'SELECT id, vat ... FROM orders WHERE id = ?';
$object = false;
if (false !== $data = conn->fetch($query, array($pk))) {
$object = new Order($data['id']);
$object->load($data);
}
return $object;
}
}
$conn = new Connection('mysql:host=localhost ...');
$mapper = new OrderMapper($conn);
$order = $mapper->find(42);
$order->setAmount(399.00);
$order->updateTotal();
$mapper->store($order);
Unit testing
class OrderTest extends PHPUnit_Framework_TestCase
{
public function testUpdateTotal()
{
$order = new Order();
$order->setAmount(299.00);
$order->setVatRate(0.196);
$order->updateTotal();
$this->assertEquals(58.60, $order->getVat());
$this->assertEquals(357.60, $order->getTotal());
}
}
When to use it?
IdentityMap
« Ensures that each object gets
loaded only once by keeping every
loaded object in a map. »
Martin Fowler
$conn = new Connection('mysql:host=localhost ...');
$mapper = new OrderMapper($conn);
$orderA = $mapper->find(42);
$orderB = $mapper->find(42);
$orderC = $mapper->find(42);
// 3 SQL queries for getting the same object
The solution
class IdentityMap implements IdentityMapInterface
{
private $entities;
public function fetch($class, $pk)
{
$key = $this->getKey($class, $pk);
if (isset($this->entities[$key])) {
return $this->entities[$key];
}
return false;
}
}
class IdentityMap implements IdentityMapInterface
{
public function store(ValueObjectInterface $entity)
{
$key = $this->getKey($class, $entity->getId());
$this->entities[$key] = $entity;
}
private function getKey($class, $pk)
{
return $class.'-'.$pk;
}
}
class Order implements ValueObjectInterface
{
private $id;
private $reference;
private $amount;
// ...
public function getId()
{
return $this->id;
}
}
class OrderMapper extends DatabaseMapper
{
private $map;
public function __construct(IdentityMap $map, ...)
{
parent::__construct($conn);
$this->map = $map;
}
}
class OrderMapper extends DatabaseMapper
{
public function store(Order $order)
{
parent::store($order);
$this->map->store('Order', $object);
}
}
class OrderMapper extends DatabaseMapper
{
public function find($pk)
{
if (false !== $object = $this->map->fetch($pk)) {
return $object;
}
if (false !== $object = parent::find($pk)) {
$this->map->store('Order', $object);
}
return $object;
}
}
$conn = new Connection('mysql:host=localhost ...');
$mapper = new OrderMapper(new IdentityMap(), $conn);
$orderA = $mapper->find(42); // Query
$orderB = $mapper->find(42); // No query
$orderB->setAmount(299.00);
$orderB->setVatRate(0.196);
$orderB->updateTotal();
$mapper->store($orderB);
$orderC = $mapper->find(42); // No query
Query Object
$query = Query::create()
->select(array('id', 'reference', 'amount', 'status'))
->from('orders')
->where(Criteria::equals('status', 'paid'))
->where(Criteria::greaterThan('amount', 2000))
->where(Criteria::like('reference', 'XX123%'))
->orderBy('amount', 'desc')
->getSql()
;
// SELECT id, reference, amount, status
// WHERE status = ? AND amount > ? AND reference LIKE ?
// ORDER BY amount DESC
class Criteria
{
private $field;
private $operator;
private $parameters;
public function __construct($field, $operator, $value)
{
$this->field = $field;
$this->operator = $operator;
$this->parameters[] = $value;
}
}
class Criteria
{
static public function equal($field, $value, $vars)
{
return new Criteria($field, '=', $vars);
}
static public function notEqual($field, $value, $vars)
{
return new Criteria($field, '<>', $vars);
}
}
Custom Queries
class OrderQuery extends Query
{
public function filterByPriority($amount)
{
return $this
->where(Criteria::equal('status', 'paid'))
->where(Criteria::greaterThan('amount', $amount))
;
}
public function filterByReference($like)
{
return $this->where(Criteria::like('reference', $like));
}
}
$query = OrderQuery::create()
->filterByPriority(2000)
->filterByReference('%567%')
->orderByAmount('DESC')
->getSql()
;
ORM Tools
Zend_DB
Doctrine 1.2
Doctrine 2.x
Propel
Pomm
Quizz
Can you guess the patterns?
$table = new Author(); // New empty row $row = $table->createRow(); // Insert a new row $row->firstName = 'Jules'; $row->lastName = 'Verne'; $row->save();
$pax1 = new Passenger('Hugo Hamon', '7B'); $pax2 = new Passenger('John Smith', '3A'); $aircraft = new Plane(); $aircraft->setCapacity(120); $aircraft->addPassenger($pax1); $aircraft->addPassenger($pax2); $aircraft->save(); $pax2->changeSeat('2C'); $pax2->save(); $aircraft->isAvailableSeat('3A') ? 'Yes' : 'No';
$post = new BlogPost(); $post->setTitle('My First Blog Post'); $post->setBody('Some content...'); $author = new Author(); $author->setName('Hugo Hamon'); $author->addPost($post); $em->persist($user); $em->persist($post); $em->flush();
$data = array( 'first_name' => 'Jules', 'last_name' => 'Vernes', ); $table = new AuthorTable(); $table->insert($data);
Conclusion
By Martin Fowler § Table Module § Transaction Script § Row Data Gateway § Table Data Gateway § Active Record § Data Mapper § Unit of Work § Identity Map § Data Transfer Object § …
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