1.
FUNCTIONAL
PROGRAMMING
Practical!
RAILS
RUBYIN
ON
BY

2.
Overview
• What is a Service Layer?
• Railway Oriented Programming
• Creating Beautifully Composable Services

3.
Whatisa
LAYER
?
SERVICE

4.
Whatisa
LAYER
SERVICE
??

5.
A Service is an object
that represents a process.

6.
A process is something you do.
• Typically initiated by the user
• Usually implemented as a dedicated class
• Named with verbs, not nouns
• Examples: SignupUser, PurchaseItem, etc.
SERVICES

7.
SignupUser
Purchase
Item
RAILS
SERVICES
SERVICE
LAYER
Payout
Account

8.
A Service in Rails
SERVICES
CODEEXAMPLE
A Service
Usage in Controller

9.
[Naive] Validations
CODEEXAMPLE
A Service
Usage in Controller
SERVICES

10.
Why a Service useful?
• It encapsulates domain logic
• It thins out your models & controllers
• It ties together cross-cutting concerns
• It makes your Rails app easier to test.
SERVICES

11.
A service layer is about clear separation.
• Rails depends on the service layer
• The service layer knows nothing about Rails
(routes, controllers, & views)
• Other things could depend on the service layer
(REST API, web sockets, rake tasks, etc.)
• ActiveRecord is unavoidable, however.
SERVICES

12.
SERVICES

13.
Quick Recap
• A service is an object that represents a process
• Services encapsulate domain logic for specific
processes
• No functional programming (yet).
SERVICES

14.
RAILWAYORIENTED
PROGRAMMING
http://fsharpforfunandprofit.com/posts/recipe-part2/

15.
Services: Another Perspective
A service is a sequence of steps
• They often involve a lot of setup
• Authentication, authorization, validation, etc.
Any one of these steps could fail
• How to handle failure??
RAILWAY

16.
Naive Validations
CODEEXAMPLE(REVISITED)
A Service RAILWAY

17.
Can we do be er?
RAILWAY
What if each step was an
independent method?
How would each step
communicate?

18.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
The “Switch”
Input→ Success!
Failure.
fetch_item
DIAGRAM

19.
RAILWAY
The “Switch”
Input→ Success!
Failure
fetch_item
CODEEXAMPLE

20.
RAILWAY
The “Switch”
Input→ Success!
Failure.
fetch_item
CODEEXAMPLE
Failure.
Success!

21.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
Our Target Flow
onsuccess
Success!
Failure.
Input→
fetch_item validate
onfailure

22.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
Our Target Flow
Success!
Failure.
Input→
create_ordervalidatefetch_item

23.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
Our Target Flow
Success!
Failure.
Input→
create_ordervalidatefetch_item
IT’DBECOOLIFWECOULDCONNECTTHESETOGETHER

24.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
Connecting Switches
Success!
Failure.
Input→
create_ordervalidatefetch_item
create_ordervalidatefetch_item

25.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
RAILWAY
Connecting Switches
Success!
Failure.
Input→
create_ordervalidatefetch_item
create_ordervalidatefetch_item
create_ordervalidatefetch_item
Success!
Failure.

26.
RAILWAY
Connecting Switches
CODEEXAMPLES
create_ordervalidatefetch_item
?? ??

27.
RAILWAY
Connecting Switches
CODEEXAMPLES
create_ordervalidatefetch_item
?? ??
HOWDOWECONNECT
ITALLTOGETHER?
?
?
?
?
?
?
?
?

28.
RAILWAY
Answer:

29.
RAILWAY
¯_(ツ)_/¯
Answer:

30.
RAILWAY
¯_(ツ)_/¯
Answer:
ITDOESN’TMATTER!

31.
RAILWAY
¯_(ツ)_/¯
Answer:
ITDOESN’TMATTER!
:D

32.
RAILWAY
¯_(ツ)_/¯
Answer:
ITDOESN’TMATTER!
:D
(actual answer: monads)

33.
There’s a gem for that!
Doesn’t matter.
RAILWAY
github.com/mindeavor/solid_use_case

34.
There’s a gem for that!
Don’t worry.

35.
Handling failures?
RAILWAY
What about
github.com/mindeavor/solid_use_case

36.
Quick Recap
• Split steps into methods
• Return a success or failure in each one
• Elegant (with gem) error handling!
• Steps can be tested independently
RAILWAY

37.
COMPOSINGSERVICES
FORMAXIMUMCOOLNESS

38.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
Remember This?
Success!
Failure
Input→
create_ordervalidatefetch_item
create_ordervalidatefetch_item
create_ordervalidatefetch_item
Success!
Failure

39.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
Input→ Success!
Failure
create_ordervalidatefetch_item
What if we treat it like a single thing…

40.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
Input→ Success!
FailurePurchaseItem
What if we treat it like a single thing…

41.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
Input→
PurchaseItem Success!
Failure
What if we treat it like a single thing…

42.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
…and then connect it to other things??
Input→
PurchaseItem
Success!
Failure

43.
Source: http://www.slideshare.net/ScottWlaschin/railway-oriented-programming
COMPOSE
Input→
PurchaseItem EmailReceipt
Success!
Failure
…and then connect it to other things??

44.
Service Composition
CODEEXAMPLE
COMPOSE

45.
Service Composition
CODEEXAMPLE
Another
Service!
COMPOSE

46.
Service Composition
CODEEXAMPLE
Another
Service!
COMPOSE

47.
Recap
• We can compose services like we can steps
(in fact we can compose anything that returns our success or failure)
• Functional programming rocks!
COMPOSE

48.
Conclusion
• Service layers are great for apps more complex
than CRUD
• Railway oriented programming is great for
seamless error handling
• Functional programming gives us composable
services!

49.
In the end,
don’t take my word for it.

50.
TRY ITYOURSELF!

51.
Thanks!
H
urrah!
END.
THE
BY
- Gilbert (@mindeavor)

52.
Further Reading
• http://martinfowler.com/eaaCatalog/serviceLayer.html
• https://gist.github.com/blaix/5764401
• http://fsharpforfunandprofit.com/posts/recipe-part2/
• The gem: https://github.com/mindeavor/solid_use_case