Domain Driven Design for Mere Mortals

Application architecture can seem like a buzzword. In this talk we will look at some useful, fundamental concepts introduced by the book on Domain Driven Design and how we as PHP developers can apply these techniques to our applications. Walking out of this talk you should have a functional understanding of how to approach designing how your applications execute business logic using DDD patterns and processes.

Transcript

1. PRESENTED BY JEFF CAROUTH @jcarouth Domain Driven Design for mere mortals
2. What is Domain Driven Design?
3. What is Domain Driven Design? A collection of patterns and principles which help developers craft elegant software.
4. disclaimer #1 Domain Driven Design was created to solve complicated problems. As such there is no way to learn it in one hour, one talk, or one deep thought.
5. Disclaimer #2 There are a lot of very complicated domains which would be served well by using DDD. There are many more that would not.
6. The three important bits
7. The three important bits 1. The Ubiquitous Language
8. The three important bits 1. The Ubiquitous Language 2. Contexts and Bounded Contexts
9. The three important bits 1. The Ubiquitous Language 2. Contexts and Bounded Contexts 3. Modeling
10. The Ubiquitous Language
11. The Ubiquitous Language A common language shared between business and developers which is understood to mean the same things, and, more importantly, is framed in business terminology rather than technical terminology.
12. The Ubiquitous Language is developed over time, during discussions between developers and domain experts.
13. The Ubiquitous Language consists of mainly words and expressions that are understood by both business experts and developers.
14. The Ubiquitous language is expressed in the code that implements the domain.
15. The Ubiquitous Language should be under constant refinement.
16. Contexts and Bounded Contexts
17. Context The term Context is a general description of a grouping of concepts.
18. bounded context A Bounded Context is an area of your application that is bounded by explicit boundaries and has its own Model and maintains its own code.
19. Context Maps Bounded Context must sometimes communicate with each other. A Context Map is the contract your Bounded Context agrees to fulfill with the outside world.
20. Modeling
21. Building Blocks
22. Building Blocks • Entities
23. Building Blocks • Entities • Value Objects
24. Building Blocks • Entities • Value Objects • Aggregates
25. Building Blocks • Entities • Value Objects • Aggregates • Repositories
26. Entities An object that is uniquely identified by an identifier or combination of its attributes.
27. class BankAccount! {! private $accountNumber;! private $routingNumber;! private $customerName;! private $customerEmail;! ! public function setAccountNumber($number)! {! $this->accountNumber = $number;! }! ! public function setRoutingNumber($number)! {! $this->accountNumber = $number;! }! }!
28. class AccountNumber! {! public function construct($routingNumber, $accountNumber)! {! //...snip...! }! }! ! class BankAccount! {! private $accountNumber;! private $customer;! ! public function __construct(AccountNumber $accountNumber, ! Customer $customer)! {! $this->accountNumber = $accountNumber;! $this->customer = $customer;! }! }
29. Value Objects An object that holds value within its state, but is indistinguishable from other objects of the same type with the same attributes.
30. class Money! {! public function __construct($value, $currency)! {! //...snip...! }! }! ! $fiveDollars = new Money(5, 'USD');! $anotherFiveDollars = new Money(5, 'USD');
31. class Customer! {! public function __construct($billingAddress, $email)! {! $this->billingAddress = $billingAddress;! $this->email = $email;! }! }
32. class Customer! {! public function __construct($billingAddress, $email)! {! if (!/* nasty email regex here*/) {! throw new \InvalidArgumentException('message');! }! }! }!
33. class Email! {! public function __construct($name)! {! if (!/* nasty email regex here*/) {! throw new \InvalidArgumentException('message');! }! $this->email = $email;! }! }! ! class Customer! {! public function __construct($billingAddress, Email $email)! {! $this->billingAddress = $billingAddress;! $this->email = $email;! }! }
34. Aggregates A group of Entities and/or Value Objects which represent a single object or idea.
35. class Order! {! /** @var string */! private $orderId;! ! /** @var Customer */! private $customer;! ! /** @var Product */! private $product;! ! /** @var PaymentStatus */! private $paymentStatus;! ! /** @var OrderLines[] */! private $lineItems;! }
36. Repositories An abstraction for persistence. A Repository can be thought of as an interface representing an in-memory data store for Entities or Aggregates.
37. interface CustomerRepository! {! public function add(Customer $customer);! ! public function remove(Customer $customer);! ! /** @return Customer */! public function find(CustomerId $customerId);! ! /** @return array */! public function findAll();! }
38. class DbCustomerRepository implements CustomerRepository! {! public function add(Customer $customer)! {! $sql = "INSERT INTO customers VALUES(...)";! //...snip...! }! }
39. Recap
40. Recap • DDD is a set of patterns and practices which help deal with business complexity in the Domain.
41. Recap • DDD is a set of patterns and practices which help deal with business complexity in the Domain. • DDD is not necessarily the right fit for every project.
42. Recap • DDD is a set of patterns and practices which help deal with business complexity in the Domain. • DDD is not necessarily the right fit for every project. • DDD wants you to think in Contexts.
43. Recap • DDD is a set of patterns and practices which help deal with business complexity in the Domain. • DDD is not necessarily the right fit for every project. • DDD wants you to think in Contexts. • DDD has building blocks that help with the implementation of your Domain Model.
44. Resources Domain Driven Design by Eric Evans is the original, more academic look into DDD. Implementing Domain Driven Design by Vaughn Vernon has a more practical approach to teaching DDD.
45. DDDinPHP Google Group Resources The Dev Book Club is reading and discussing the IDDD book. Discussion group focusing on applying DDD to PHP projects. devbookclub.org dddinphp.org
46. Thank You @jcarouth joind.in/10804