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Domain-Driven Design - True North PHP 2016

Domain-Driven Design - True North PHP 2016

Andrew Cassell

November 04, 2016
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  1. Domain-driven
    Design
    Deconstructed
    Domain-driven
    Design
    Deconstructed
    Andrew Cassell

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  7. Domain-Driven
    Design

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  12. Domain-Driven
    Design

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  13. DDD

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  17. 18

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  19. People don't want to buy a quarter-inch
    drill, they want a quarter-inch hole.
    Theodore Levitt

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  20. Domain

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  21. Domain

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  22. Penn State Pattee Library

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  23. book
    user
    book_inventory
    book_inventory_user_link
    ROLE_USER
    ROLE_ADMIN

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  24. Source: http://jonclaytonbiz.com/

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  26. #DDD4ME

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  31. Common Sense
    Software
    Development

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  32. http://www.sei.cmu.edu/reports/95tr021.pdf

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  34. DDD BALL OF MUD/CRUD
    Correctness
    Testability
    Usability
    Maintainability
    Modifiability

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  35. Performance

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  37. Security

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  38. DDD Common
    Misconceptions

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  46. CRUD is okay-ish

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  51. Ubiquitous
    Language

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  52. Ubiquitous Language
    Developers
    Domain
    Experts

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  55. Ubiquitous
    Language

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  56. User
    Customer
    Client
    Member
    Affiliate

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  57. 1. Naming Things
    2. Cache Invalidation
    3. Off By One Errors
    Top 10 Reasons
    Programming is Hard

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  58. DDD CRUD/MUD
    Members Users
    LibraryCatalog BookRepository
    ISBN String
    DeweyDecimal Float(7,3)

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  59. $user = User::findOrFail($uuid);

    $book = Books::where('isbn', '=', $isbn)->take(1)->get();



    if (!$user->userBookLinks()->contains($book->id) && $user->borrowLinks->count() < 5) {


    $user->userBookLinks()->attach($book->id, ['date_due' => new DateTime('+2 Weeks')];


    }



    $user->save();

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  61. $catalog = new LibraryCatalog(…);
    $book = $catalog->findOneBookByISBN($isbn);
    $members = new Members(…);
    $borrower = $members->findOneByAccountNumber($id);
    $borrower->borrow($book);
    $members->updateAccount($borrower);

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  62. $borrower->borrow($book);
    $borrower->loan($book);
    $borrower->obtain($book);
    $borrower->take($book);

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  63. DDD BALL OF MUD/CRUD
    Correctness ✓
    Testability
    Usability
    Maintainability
    Modifiability

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  66. Sales
    Marketing
    Finance
    Production

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  67. Customer
    Lead
    Payee
    ShipTo

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  68. Slide: Vaughn Vernon

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  72. Alberto Brandolini

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  73. http://ziobrando.blogspot.be/

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  80. 7 Dirty Words When Meeting With a Domain Expert
    1.Session
    2.Repository
    3.Abstract
    4.Interface
    5.Class
    6.Database
    7.Foreign Key

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  83. User Research

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  84. Photo: Mathias Verraes

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  97. Domain Objects
    Repositories
    Commands & Command handlers
    Business rules/specifications
    Messages
    Domain events

    Aggregates
    Entities
    Value Objects
    Invariants
    Processes

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  98. Domain Objects
    Repositories
    Commands & Command handlers
    Business Rules/Specifications
    Messages
    Domain Events

    Aggregates
    Entities
    Value Objects
    Invariants
    Processes

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  99. Value Object
    Immutable
    No Identity (Only Values)
    Entity
    Mutable
    Has A Lifecycle
    Always Stable
    Contains Value Objects
    Aggregate
    Entity
    Responsible For Child Entities

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  100. Value Objects
    Amount Paid
    Email Address
    BookTitle
    Dewey Decimal Number
    ISBN Number

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  101. Immutability
    Avoid Spooky
    Action at a
    Distance

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  102. Value Objects

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  103. Not Just Static Typing
    https://github.com/Fiedzia/type-system-research/blob/master/README.md
    Value Objects

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  104. “Gateway Drug to
    Test Driven Development”
    Value Objects

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  105. “Gateway Drug to
    Test Driven Development”
    Value Objects
    #MYTESTSDONTPASS

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  106. Value Objects
    ALWAYS IN A
    VALID STATE

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  107. Plain PHP Objects (POPOs)
    •Declare Class Properties as Private
    •No Setters
    •All Parameters Are Injected in the Constructor
    •Do Not Store References to Mutable Objects (Private Scalars Okay)
    •Throw Exceptions If Something Is Wrong
    •Functions that Appear to Modify Should Return a New Object
    •Declare the Class Final so it can’t be Overridden (probably)
    Value Objects

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  108. Example
    BookTitle

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  116. Example
    BookCondition

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  121. Example
    DateBorrowed

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  123. Example
    DateDue

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  125. Example
    LoanPeriod

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  127. DDD CRUD/MUD
    BookTitle String
    BookCondition String
    ISBN String
    DeweyDecimal Float(7,3)
    DateBorrowed DateTime

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  128. DDD BALL OF MUD/CRUD
    Correctness ✓
    Testability ✓
    Usability
    Maintainability
    Modifiability

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  130. Identifiable
    Has State and is Mutable
    Never Invalid State
    Required Parameters Passed in Constructor
    Operates Using Value Objects
    No Security or Permission Checks
    Storage Agnostic
    Entities

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  131. Entities
    Librarian
    Book

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  134. SETTERS
    ARE BAD

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  141. Doctrine

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  143. •Special Kind of Entity
    •Manages Child Entities
    •Transactionally Safe
    Aggregates

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  144. Aggregates
    Member
    Fines Invoice

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  150. Task Based
    User Interface

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  153. DDD BALL OF MUD/CRUD
    Correctness ✓
    Testability ✓
    Usability ✓
    Maintainability
    Modifiability

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  154. Security

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  155. Domain
    (Business Logic)
    Application
    Services
    Controller
    Persistence
    Event/Command Bus
    Security
    Templates

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  156. Controller
    Domain
    Framework

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  161. Controller
    Domain
    Framework

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  162. Mathias Verraes - Decoupling the Model from the Framework at Laracon EU 2014
    https://www.youtube.com/watch?v=QaIGN_cTcc8

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  163. Ruby Midwest 2011 - Keynote: Architecture the Lost Years by Robert Martin
    https://www.youtube.com/watch?v=WpkDN78P884

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  164. Domain
    (Business Logic)
    Application
    Services
    Controller
    Persistence
    Event/Command Bus
    Security
    Templates

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  165. DDD BALL OF MUD/CRUD
    Correctness ✓
    Testability ✓
    Usability ✓
    Maintainability ✓
    Modifiability

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  166. Domain
    Events

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  167. Domain Events
    •Something That Happened In The Past
    •Immutable Value Objects
    •Part of the Core Domain
    •Usually Created in an Aggregate
    •Probably Want To Persist Them
    •Passed to Event Bus (Application Layer)
    •Listeners are Application Services
    •Used To Cross Bounded Contexts
    •Do Not Contain Entities (Only Value Objects)

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  171. BookWasOverdue

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  173. DDD BALL OF MUD/CRUD
    Correctness ✓
    Testability ✓
    Usability ✓
    Maintainability ✓
    Modifiability ✓

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  174. Command Query
    Responsibility
    Segregation

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  175. CQRS

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  176. Slide: Microsoft

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  181. https://gnugat.github.io/
    2016/05/11/towards-cqrs-
    command-bus.html

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  185. Controller
    Domain
    Framework

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  186. Event
    Sourcing

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  187. Event Sourcing
    •Store the Events That Happen
    •Append Only Event Storage
    •Object Properties are Not Stored

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  191. Event Sourcing
    •Avoids Data Mapping
    •Avoids Object-relational Impedance Mismatch
    •Reduces Database Table Counts (Related Tables)
    •Potentially Reduces Model Counts

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  192. Slide: Microsoft

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  196. Libraries
    •https://github.com/szjani/predaddy
    •https://github.com/prooph
    •https://github.com/qandidate-labs/broadway

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  197. Learning
    More

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  199. DevBookClub
    https://www.youtube.com/user/devbookclub

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  205. DDDinPHP
    Google Group
    http://DDDinPHP.org

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  208. Manage Private Internal
    Dependencies With
    Composer and Satis

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  209. https://joind.in/talk/82ad0
    Topics Covered
    •Ubiquitous Language
    •Event Storming
    •Modelling
    •Value Objects
    •Entities
    •Aggregates
    •Hexagonal Architecture
    •CQRS
    •Event Sourcing

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