Defensive Code Design @ Phpro weekend

In this presentation, I'll take you through a journey of "How to make changing a username complex …".
We'll discover some design patterns together whilst refactoring a legacy god controller into smaller well designed chunks.
Will the result actually be complexer? Come and find out!

In a second chapter, we'll handle some insane never-changing business requirements together. Spoiler alert: The requirements will change ...

Parental Advisory : The presentation will contain random memes and buzzwords like : hexagonal architecture, commandbus, functional programming, immutability, pure functions, ...

Transcript

2. What  does  it  mean  to  YOU?
3. How  do  YOU  use  it  today?
4. How  would  YOU  like  to  use  it  tomorrow?
5. A  Journey  …. How  to  make  "changing  a  username"  complex  …
6. Let's  go  back  in  time
11. Question  :   How  can  we Improve  the  code  structure  ?
13. Achievement  unlocked! HEXAGONAL  DESIGN
15. Question  :   Where  do  we  place the  controller  ?
16. Question  :   Where  will  we  change the  userName?
17. Question  :   How  can  the  controller change  the  userName?
18. ChangeUsername Command COMMAND  BUS ChangeUsername Command  Handler
20. Achievement  unlocked! THE  COMMAND  PATTERN
22. COMMAND  BUS (Multiplexer) ChangeUsername Command  Handler FireEmployee Command  Handler GrantBonus Command  Handler ChangeUsername Command
23. Achievement  unlocked! THE  SERVICE  LAYER
24. Question  :   Where  do  we  place the  command?
25. Question  :   Where  do  we  place  the command  handler?
26. Question  :   Where  do  we  place  the command  bus?
29. Achievement  unlocked! THE  BRIDGE  PATTERN
32. Achievement  unlocked! THE  REPOSITORY  PATTERN
33. Database UserRepository UserRepository Interface InMemory UserRepository CSV UserRepository
35. Achievement  unlocked! INVERSION  OF  CONTROL  PATTERN
36. Question  :   Where  do  we  place repositories?
37. Question  :   What  if  we  wanted  to cache  data?
38. Database UserRepository UserRepository Interface Caching UserRepository
40. Achievement  unlocked! THE  DECORATOR  PATTERN
43. Question  :   Where  do  we  place  the validation?
44. ChangeUsername Command COMMAND  BUS ChangeUsername Command  Handler Validation Middleware
45. Achievement  unlocked! THE  MIDDLEWARE  PATTERN
46. UserNameExists Rule Symfony UserNameAllowed Constraint CommandBus SymfonyValidator Middleware UserNameContains NoSwearWords Rule
48. Question  :   Where  do  we  place  the logging?
49. ChangeUsername Command COMMAND  BUS ChangeUsername Command  Handler Validation Middleware Logger Middleware
52. Question  :   Where  do  we  place  the Security  voters?
53. ChangeUsername Command COMMAND  BUS ChangeUsername Command  Handler Security Middleware Logger Middleware Validator Middleware
54. UserIsBlocked Rule Symfony Change UserName Voter CommandBus SymfonySecurity Middleware UserIsOwner Rule
57. Question  :   Where  do  we  place  the emailing?
59. Question  :   Where  do  we  place  the event  dispatcher?
60. Question  :   Where  do  we  place  the event?
62. Achievement  unlocked! THE  DOMAIN  EVENT
63. Question  :   Where  do  we  place  the event  listeners?
67. Achievement  unlocked! THE  OBSERVER  PATTERN
68. Question  :   What  if  we  needed  to sync  the  user?
70. Domain Models 3rd Party System Adapter Transformations
72. Achievement  unlocked! THE  ADAPTER  PATTERN
73. Question  :   Dude  …  you  are  very  optimistic  about  the   connection How  can  we  log  stuff?
74. SomeCrm\Client ::syncUser() HTTP  /  SOAP  Client SOME  CRM SERVER Logger Middleware
75. Question  :   That  is  ok,  but  what  about ACTUAL  error  handling?
81. Question  :   Syncing  can  be  so  SLOOOW What  can  we  do  about  it?
82. ASYNC COMMAND  BUS ASYNC EVENT  DISPATCHER ASYNC HANDLER  /  LISTENER JOBS  Monitor Message  Queue ASYNC LISTENER
84. Question  :   How  can  we  handle  urgent  exceptions?
85. Level Urgency Notification Debug / / Info / / Notice / / Warning / / Error 1d / Critical 2-­‐4h Push Alert 2h Push Emergency <1h Push
87. Question  :   How  do  we  handle  errors?
89. https://github.com/phpro/api-­‐problem https://github.com/phpro/api-­‐problem-­‐bundle
95. Positive: • Every  function  does  1  thing • Every  class  does  1  thing • Easy  to  test • Easy  to  debug • Easy  to  extend Negative: • We  made  a  simple  task   complex  (but  not  really) • It  takes  a  lot  of  boilerplate   code • You  have  to  know  what  you   are  doing!
96. Question  :   How  do  we Fetch  data?
101. Question  :   How  do  we  handle Critical  Business  Rules?
102. Example  :   The  total  price  of  an  invoice is  20  EUR  per  invoiced  items.
104. Example  :   total  =  20  *  count(invoice.items)
107. Achievement  unlocked! PURE  FUNCTIONS
109. Next  feature  request:   Please  make  it  25  EUR  per  invoice  line! Ah  yea:  only  the  even  lines  count
116. Achievement  unlocked! FUNCTION  COMPOSITION
117. Next  feature  request:   When  an  invoice  is  created We  want  to  log  some  statistics
123. Achievement  unlocked! IMMUTABILITY