Domain-driven Design in PHP and Symfony - Drupal Camp Wrocław 18/10/2014 More Domain-Driven Design related content at: https://domaincentric.net/

1. Domain-Driven Design
in PHP & Symfony

2. Kacper Gunia @cakper
Software Engineer @SensioLabsUK
Symfony Certified Developer
PHPers Silesia @PHPersPL

4. Software is complex

6. How to tackle it?

7. Domain-Driven Design is !
an approach to the
development of complex
software in which we:
–Eric Evans

8. 1. Focus on the core domain.
–Eric Evans

9. 2. Explore model in !
a creative collaboration of
domain practitioners and
software practitioners.
–Eric Evans

10. 3. Speak an ubiquitous
language within an
explicitly bounded context.
–Eric Evans

11. When to use DDD?

12. Complex domain

13. Domain Experts

14. Iterative process

15. Object-Oriented Design

16. Strategic DDD

17. Strategy!
!
Stratos - army/resources!
Ago - leading

18. Strategy!
!
!
= What

19. Bounded Context

20. Bounded contexts of product
❖ Catalogue!
❖ Sales!
❖Marketing!
❖Warehouse

21. Ubiquitous language

22. Core Domain

23. Supporting Domain

24. Model-Driven Design

25. Continuous Integration

26. UI
SERVICE
UNIT

27. Refactoring Towards
Deeper Insight

28. Tactical DDD

29. Tactics!
!
Taktike - the art of organising
an army, a maneuver

30. Tactics!
!
!
= How

31. Building Blocks

32. Layered architecture

33. USER INTERFACE
APPLICATION
DOMAIN
INFRASTRUCTURE

34. .
└──
src
└──
Dcwroc
├──
Shopping
├──
Emejzon
├──
EmejzonBundle
└──
DoctrineAdapter

35. Entities

36. class
Sale
{
(…)
private
$id;
!
function
__construct($name,
DateTimeInterface
$dueDate)
{
$this-­‐>name
=
$name;
$this-­‐>dueDate
=
$dueDate;
}
!
public
function
getId()
{
return
$this-­‐>id;
}
}

37. class
Sale
{
(…)
public
function
activate()
{
if
(true
===
$this-­‐>active)
{
throw
new
LogicException('Sale
already
activated!');
}
!
$this-­‐>active
=
true;
}
}

38. Value objects

39. class
Email
{
(…)
public
function
__construct($email)
{
if
(!filter_var($email,
FILTER_VALIDATE_EMAIL))
{
throw
new
InvalidArgumentException();
}
!
$this-­‐>email
=
$email;
}
!
function
asString()
{
return
$this-­‐>email;
}
}

40. Aggregates

41. class
Order
{(…)
function
__construct(
Customer
$customer,
ProductList
$productList
){
$this-­‐>customer
=
$customer;
$this-­‐>productList
=
$productList;
$this-­‐>status
=
Status::open();
}
!
public
function
getTotal();
}

42. Repositories

43. interface
OrderRepository
{
public
function
save(Order
$order);
!
public
function
remove(Order
$order);
public
function
findById($orderId);
!
public
function
findObsolete();
}

44. class
DoctrineOrderRepository
implements
OrderRepository
{}
!
class
FileOrderRepository
implements
OrderRepository
{}
!
class
InMemoryOrderRepository
implements
OrderRepository
{}

45. Factories

46. class
CustomerFactory
{
public
function
register(Email
$email,
Password
$password)
{
(...)
!
return
$customer;
}
}

47. Services

48. interface
Notifier
{
public
function
send(Message
$message);
}

49. class
EmailNotifier
implements
Notifier
{
private
$mailer;
!
function
__construct(Swift_Mailer
$mailer)
{
$this-­‐>mailer
=
$mailer;
}
!
public
function
send(Message
$message)
{
(…)
}
}

50. Domain Events

51. class
ResetPassword
{
function
request(Email
$email)
{
$user
=
$this-­‐>userRepository-­‐>findOneByEmail($email);
!
if
(!$user
instanceof
User)
{
return
$this-­‐>raise(new
UserDoesNotExistEvent($email));
}
!
$request
=
Password::requestReset($user);
$this-­‐>passwordResetRequestRepository-­‐>save($request);
$this-­‐>raise(new
RequestIssuedEvent($request));
}
}

52. class
ResetPassword
{
function
request(Email
$email)
{
$user
=
$this-­‐>userRepository-­‐>findOneByEmail($email);
!
if
(!$user
instanceof
User)
{
return
$this-­‐>raise(new
UserDoesNotExistEvent($email));
}
!
$request
=
Password::requestReset($user);
$this-­‐>passwordResetRequestRepository-­‐>save($request);
$this-­‐>raise(new
RequestIssuedEvent($request));
}
}

53. class
ResetPassword
{
function
request(Email
$email)
{
$user
=
$this-­‐>userRepository-­‐>findOneByEmail($email);
!
if
(!$user
instanceof
User)
{
return
$this-­‐>raise(new
UserDoesNotExistEvent($email));
}
!
$request
=
Password::requestReset($user);
$this-­‐>passwordResetRequestRepository-­‐>save($request);
$this-­‐>raise(new
RequestIssuedEvent($request));
}
}

54. class
ResetPassword
{
function
request(Email
$email)
{
$user
=
$this-­‐>userRepository-­‐>findOneByEmail($email);
!
if
(!$user
instanceof
User)
{
return
$this-­‐>raise(new
UserDoesNotExistEvent($email));
}
!
$request
=
Password::requestReset($user);
$this-­‐>passwordResetRequestRepository-­‐>save($request);
$this-­‐>raise(new
RequestIssuedEvent($request));
}
}

55. Modules

56. .
└──
Shopping
└──
Authentication
├──
InvalidPasswordResetRequest.php
├──
ResetPassword.php
├──
PasswordResetRequest.php
└──
PasswordResetRequestRepository.php

57. Supple Design

58. Make behaviour obvious

59. Intention revealing
interfaces

60. Design for change

61. Create software other
developers want
to work with

62. Ignore persistance

63. Domain model is always
in a valid state

64. Command Pattern

65. class
ChangeEmailCommand
{
public
$email;
public
$customerId;
}

66. class
ChangeEmailCommandHandler
{
private
$customerRepository;
!
function
__construct(CustomerRepository
$customerRepository)
{
$this-­‐>customerRepository
=
$customerRepository;
}
!
public
function
handle(ChangeEmailCommand
$command)
{
$customer
=
$this-­‐>customerRepository
-­‐>findById($command-­‐>customerId);
$customer-­‐>changeEmail($command-­‐>email);
}
}

67. Specification Pattern

68. interface
Specification
{
public
function
isSatisfiedBy($object);
}

69. class
PayingCustomerSpecification
implements
Specification
{
public
function
isSatisfiedBy($object)
{
return
$object
instanceof
Customer
&&
$object-­‐>getAmountSpent()
>
0.0;
}
}

70. class
FreeDeliveryCalculator
{
private
$specification;
!
function
__construct(Specification
$specification)
{
$this-­‐>specification
=
$specification;
}
!
public
function
applyDiscount(Order
$order)
{
$customer
=
$this-­‐>$order-­‐>getCustomer();
if
($this-­‐>specification-­‐>isSatisfiedBy($customer))
{
$order-­‐>deliverForFree();
}
}
}

71. class
FreeDeliveryCalculator
{
private
$specification;
!
function
__construct(Specification
$specification)
{
$this-­‐>specification
=
$specification;
}
!
public
function
applyDiscount(Order
$order)
{
$customer
=
$this-­‐>$order-­‐>getCustomer();
if
($this-­‐>specification-­‐>isSatisfiedBy($customer))
{
$order-­‐>deliverForFree();
}
}
}

72. Command-Query
Responsibility
Segregation

73. Commands

74. Use ORM to fetch/save
aggregate roots

75. Queries

76. Use specialised queries
and DTO’s to fetch
presentation data

77. DDD Summary

78. Explore
Domain Knowledge

79. With Domain Experts

80. By speaking
Ubiquitous Language

81. Make use of
Building Blocks

82. By applying
Object-Oriented Design

83. Design for change

84. That’s the only constant!

85. “In order to create good
software, you have to
know what that software
is all about.”
–Eric Evans

86. Kacper Gunia
Software Engineer
Thanks!
Symfony Certified Developer
PHPers Silesia