Domain-Driven Design

Talk given at PHP Serbia 2017:
(http://www.conf2017.phpsrbija.rs/)

Transcript

1. Domain-Driven
   Design
   Deconstructed
   Domain-Driven
   Design
   Deconstructed
   Andrew Cassell
   @alc277 andrewcassell.com
   

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6. Domain-Driven
   Design
   

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7. Domain-Driven
   Design
   

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14. Domain
    

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15. Domain
    

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16. Penn State Pattee Library
    

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17. book
    user
    book_inventory
    book_inventory_user_link
    ROLE_USER
    ROLE_ADMIN
    

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18. Source: http://jonclaytonbiz.com/
    

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

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24. Common Sense
    Software
    Development
    

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25. DDD !=
    

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32. DDD CRUD
    Correctness
    Testability
    Usability
    Maintainability
    Modifiability
    

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

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38. Ubiquitous
    Language
    

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39. Ubiquitous Language
    Developers
    Domain
    Experts
    

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40. Ubiquitous
    Language
    

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41. User
    Customer
    Client
    Member
    Employee
    

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

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

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45. $user = User::findOrFail($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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47. $catalog = new LibraryCatalog(…);
    $book = $catalog->findOneBookByISBN($isbn);
    $members = new Members(…);
    $borrower = $members->findOneByAccountNumber($acctNumber);
    $borrower->borrow($book);
    

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48. $borrower->borrow($book);
    $borrower->loan($book);
    $borrower->obtain($book);
    $borrower->rent($book);
    

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49. @library @loan
    Feature: A member should be able to borrow a book
    Scenario: Member borrows a book
    Given I am authenticated as a librarian
    And I am on “/member/behat-123"
    And I press "Borrow Book"
    And I fill out form with:
    | ISBN |
    | 978-032-112521-7 |
    Then I see "Domain-driven Design"
    

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50. @library @loan
    Feature: A member should be able to borrow a book
    Scenario: Member borrows a book
    Given I am authenticated as a librarian
    And I am on “/member/behat-123"
    And I press "Borrow Book"
    And I fill out form with:
    | ISBN |
    | 978-032-112521-7 |
    Then I see "Domain-driven Design"
    

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51. […], we want to establish the idea
    that a computer language is not
    just a way of getting a computer
    to perform operations but rather
    that it is a novel formal medium
    for expressing ideas about
    methodology. Thus, programs
    must be written for people to
    read, and only incidentally for
    machines to execute.
    

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

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57. Sales
    Marketing
    Finance
    Production
    

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58. Customer
    Lead
    Payee
    ShipTo
    

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59. Slide: Vaughn Vernon
    

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61. Billing Loan Catalog
    

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62. Billing Loan Catalog
    

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63. Billing Loan Catalog
    Message
    

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64. Billing Loan Catalog
    Domain Event
    

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70. 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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71. User Research
    

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72. Photo: Mathias Verraes
    

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

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80. Domain Objects
    Value Objects
    Entities
    Aggregates
    Domain Events
    

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81. Value Object
    Immutable
    No Identity (Only Values)
    Book Title
    Amount Paid
    ISBN Number
    Entity
    Identifiable
    Mutable
    Lifecycle
    Contains Value Objects
    Book
    Librarian
    Invoice
    Aggregate
    Entity
    Responsible For Child Entities
    Transaction Boundary
    Member
    Library
    

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82. Book Title
    Dewey Decimal Number
    Date Borrowed
    ISBN Number
    Email Address
    Value Objects
    

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83. BookTitle
    DeweyDecimalNumber
    DateBorrowed
    ISBNNumber
    EmailAddress
    Value Objects
    

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

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85. Immutable
    Avoid Spooky
    Action at a
    Distance
    

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86. ALWAYS IN A
    VALID STATE
    Value Objects
    

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87. Value Objects
    

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

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

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90. Plain PHP Objects
    (POPOs)
    Value Objects
    

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91. Plain PHP Objects (POPOs)
    • Declare Class Properties as Private
    • No Setters
    • No References to Mutable Objects
    • Throw Exceptions in Constructor
    Value Objects
    

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92. BookTitle
    Example
    

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100. DateBorrowed
     Example
     

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102. RenewalsRemaining
     Example
     

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105. Example
     LoanPeriod
     

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

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

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111. Librarian
     Library
     Book
     Entities
     

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112. Identifiable
     Have State and are Mutable
     Never Invalid State
     Operate Using Value Objects
     No Security or Permission Checks
     Storage Agnostic
     Entities
     

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117. Doctrine
     

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121. SETTERS
     ARE BAD
     

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127. • Special Kind of Entity
     • Manages Child Entities
     • Transaction Boundary
     Aggregates
     

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128. Aggregates
     Member
     FinesInvoice
     

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134. Task Based
     User Interface
     

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

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139. Security
     

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

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141. Controller
     Domain
     Framework
     

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146. Controller
     Domain
     Framework
     

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

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

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

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

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151. Domain
     Events
     

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152. Domain Events
     • Part of the Core Domain
     • Happened In The Past
     • Important Enough To Record (Persist)
     • Important Enough To Concern Other Bounded Contexts
     • Immutable Value Objects
     • Do Not Contain Entities or Other Mutable Objects
     • Can Be Created in an Entity
     

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157. DamagedBookWasRemovedFromCirculation
     

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158. DamagedBookWasRemovedFromCirculation
     

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

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165. Command Query
     Responsibility
     Segregation
     

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166. CQRS
     

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167. Write Read
     

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168. Write
     Model
     Read
     Model(s)
     

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169. Write
     Domain
     Model
     Read
     Model(s)
     

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170. Controller
     Command Bus
     Handler Handler Handler
     

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171. Controller
     Command Bus
     Handler Handler Handler
     Request
     

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172. Controller
     Command Bus
     Handler Handler Handler
     Command
     

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174. Controller
     Command Bus
     Handler Handler Handler
     Command
     

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175. Controller
     Command Bus
     Handler Handler Handler
     Command
     

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176. Controller
     Command Bus
     Handler Handler Handler
     Command
     

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177. Controller
     Command Bus
     Handler Handler Handler
     Response
     

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178. Controller
     Command Bus
     Handler Handler Handler
     Response
     

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179. Controller
     Command Bus
     Handler Handler Handler
     Response
     

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180. Controller
     Domain
     Framework
     

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

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183. Event
     Sourcing
     

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

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188. Event Sourcing
     • Object Properties are Not Persisted
     • Events Are Persisted to Append
     Only Event Storage
     

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192. Libraries
     • https://github.com/broadway
     • https://github.com/prooph
     • https://github.com/szjani/predaddy
     

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193. Learning
     More
     

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195. DEV BOOK CLUB
     https://www.youtube.com/user/devbookclub
     

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

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203. https://joind.in/talk/e8752
     DDD Topics Covered
     •Ubiquitous Language
     •Event Storming
     •Modelling
     •Value Objects
     •Entities
     •Aggregates
     •Hexagonal Architecture
     •CQRS
     •Event Sourcing
     

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