Download - Unbreakable Domain Models - FrOSCon 2013
UnbreakableDomain Models
Mathias Verraes
FrOSConSankt-Augustin, DE
August 24, 2013
@mathiasverraeshttp://verraes.net
I'm an independent consultant.
I build enterprise web applications.
I help teams escape from
survival mode.
Cofounder of theBelgian
Domain-Driven Design community
http://domaindriven.be@DDDBE
Modellathon on September 3rd, 2013
Ghent
DomainProblem Space
Domain ModelSolution Space
(Data ModelThe model’s state)
Protect your invariants
The domain expert says
“A customer must always have an email address.”
* Could be different for your domain** All examples are simplified
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_an_email() {
$customer = new Customer();
assertThat( $customer->getEmail(), equalTo('[email protected]') );
}}
Test fails
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_an_email() {
$customer = new Customer(); $customer->setEmail('[email protected]'); assertThat( $customer->getEmail(), equalTo('[email protected]') ); }}
Test passes
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_an_email() {
$customer = new Customer(); assertThat( $customer->getEmail(), equalTo(‘[email protected]') ); $customer->setEmail(‘[email protected]’);
}}
Test fails
class Customer{ private $email;
public function __construct($email) { $this->email = $email; }
public function getEmail() { return $this->email; }}
Test passes
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_an_email() {
$customer = new Customer(‘[email protected]’);
assertThat( $customer->getEmail(), equalTo(‘[email protected]') ); }}
Test passes
Use objects asconsistency boundaries
class ProspectiveCustomer { //...
/** @return PayingCustomer */ public function convertToPayingCustomer(){ }}
class PayingCustomer { ... }
Make the implicitexplicit
The domain expert meant
“A customer must always have a valid
email address.”
$customerValidator = new CustomerValidator;if($customerValidator->isValid($customer)){ // ...}
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_a_valid_email() {
$this->setExpectedException( '\InvalidArgumentException' );
new Customer('malformed@email');
}}
Test fails
class Customer { public function __construct($email) { if( /* ugly regex here */) { throw new \InvalidArgumentException(); } $this->email = $email; }}
Test passes
ViolatesSingle Responsibility
Principle
class Email{ private $email;
public function __construct($email) { if( /* ugly regex here */) { throw new \InvalidArgumentException(); } $this->email = $email; }
public function __toString() { return $this->email; } }
Test passes
class Customer{ /** @var Email */ private $email;
public function __construct(Email $email) { $this->email = $email; }}
Test passes
class CustomerTest extends PHPUnit_Framework_TestCase{ /** @test */ public function should_always_have_a_valid_email() {
$this->setExpectedException( ‘\InvalidArgumentException’ );
new Customer(new Email(‘malformed@email’));
}}
Test passes
Encapsulate state and behaviorwith Value Objects
The domain expert says
“A customer orders products
and pays for them.”
$order = new Order;$order->setCustomer($customer);$order->setProducts($products);$order->setStatus(Order::UNPAID);
// ...
$order->setPaidAmount(500);$order->setPaidCurrency(‘EUR’);
$order->setStatus(Order::PAID);
$order = new Order;$order->setCustomer($customer);$order->setProducts($products);$order->setStatus( new PaymentStatus(PaymentStatus::UNPAID));
$order->setPaidAmount(500);$order->setPaidCurrency(‘EUR’);
$order->setStatus( new PaymentStatus(PaymentStatus::PAID));
$order = new Order;$order->setCustomer($customer);$order->setProducts($products);$order->setStatus( new PaymentStatus(PaymentStatus::UNPAID));
$order->setPaidMonetary( new Money(500, new Currency(‘EUR’)));$order->setStatus( new PaymentStatus(PaymentStatus::PAID));
$order = new Order($customer, $products);// set PaymentStatus in Order::__construct()
$order->setPaidMonetary( new Money(500, new Currency(‘EUR’)));$order->setStatus( new PaymentStatus(PaymentStatus::PAID));
$order = new Order($customer, $products);
$order->pay( new Money(500, new Currency(‘EUR’)));// set PaymentStatus in Order#pay()
Encapsulate operations
$order = $customer->order($products);
$customer->pay( $order, new Money(500, new Currency(‘EUR’)));
The domain expert says
“Premium customers get special offers.”
if($customer->isPremium()) { // send special offer}
The domain expert says
“Order 3 times to become a
premium customer.”
interface CustomerSpecification { /** @return bool */ public function isSatisfiedBy(Customer $customer); }
class CustomerIsPremium implements CustomerSpecification { private $orderRepository; public function __construct( OrderRepository $orderRepository ) {...}
/** @return bool */ public function isSatisfiedBy(Customer $customer) { $count = $this->orderRepository->countFor($customer); return $count >= 3; }}
$customerIsPremium = new CustomerIsPremium($orderRepository)if($customerIsPremium->isSatisfiedBy($customer)) { // send special offer}
$customerIsPremium = new CustomerIsPremium;
$aCustomerWith2Orders = ...$aCustomerWith3Orders = ...
assertFalse( $customerIsPremium->isSatisfiedBy($aCustomerWith2Orders));
assertTrue( $customerIsPremium->isSatisfiedBy($aCustomerWith3Orders));
The domain expert says
“Different rules apply for different tenants.”
interface CustomerIsPremium extends CustomerSpecification
class CustomerWith3OrdersIsPremium implements CustomerIsPremium
class CustomerWith500EuroTotalIsPremium implements CustomerIsPremium
class CustomerWhoBoughtLuxuryProductsIsPremium implements CustomerIsPremium
...
class SpecialOfferSender{ private $customerIsPremium;
public function __construct( CustomerIsPremium $customerIsPremium) {...}
public function sendOffersTo(Customer $customer) { if($this->customerIsPremium->isSatisfiedBy( $customer )) { // send offers... } }}
<!-- if you load services_amazon.xml: --><service id="customer.is.premium" class="CustomerWith500EuroTotalIsPremium">
<!-- if you load services_ebay.xml: --><service id="customer.is.premium" class="CustomerWith3OrdersIsPremium">
<!-- elsewhere --><service id=”special.offer.sender” class=”SpecialOfferSender”> <argument type=”service” id=”customer.is.premium”/></service>
Use specifications to encapsulate rules
about object selection
The domain expert says
“Get a list of all premium customers.”
interface CustomerRepository{ public function add(Customer $customer);
public function remove(Customer $customer); /** @return Customer */ public function find(CustomerId $customerId);
/** @return Customer[] */ public function findAll();
/** @return Customer[] */ public function findRegisteredIn(Year $year);}
interface CustomerRepository{
/** @return Customer[] */ public function findSatisfying( CustomerSpecification $customerSpecification );
}
// generalized:$objects = $repository->findSatisfying($specification);
class DbCustomerRepository implements CustomerRepository{ /** @return Customer[] */ public function findSatisfying( CustomerSpecification $customerSpecification) { // filter Customers (see next slide) }}
// class DbCustomerRepository
public function findSatisfying($specification) { $foundCustomers = array(); foreach($this->findAll() as $customer) { if($specification->isSatisfiedBy($customer)) { $foundCustomers[] = $customer; } } return $foundCustomers;}
class CustomerWith3OrdersIsPremium implements CustomerSpecification{ public function asSql() { return ‘SELECT * FROM Customer...’; }}
// class DbCustomerRepository public function findSatisfying($specification) { return $this->db->query($specification->asSql()); }
Use double dispatchto preserve encapsulation
$expectedCustomers = // filtered using isSatisfiedBy$actualCustomers = $repository->findSatisfying($specification);
assertThat($expectedCustomers, equalTo($actualCustomers));
Test by comparing different representations
Protect your invariants
Objects as consistency boundaries
Encapsulate state and behavior
More? google for:Eric Evans
Vaugh VernonMartin Fowler
Greg YoungUdi Dahan
Sandro MarcusoYves Reynhout
Szymon PobiegaAlberto Brandolini
...
Thanks! Questions?
@mathiasverraeshttp://verraes.net
https://joind.in/9020
