Domain Driven Rails

@skwp @reverbdotcom #wcr14 Yan Pritzker CTO, Reverb.com  @skwp @reverbdotcom Domain
Driven Rails https://speakerdeck.com/skwp

@skwp @reverbdotcom #wcr14 Are you happy with the   SIZE
and COMPLEXITY   of your models?

@skwp @reverbdotcom #wcr14 Are you happy with the   SCALABILITY 
of your team?

@skwp @reverbdotcom #wcr14 Are you happy with the   ADAPTABILITY 
of your business?

@skwp @reverbdotcom #wcr14 What are you building?

@skwp @reverbdotcom #wcr14 Rails is a detail!" Decouple all things"
Is the code better?" Keep it Railsy"

@skwp @reverbdotcom #wcr14 Somewhere in between Simple  CRUD" Apps" Complex 
Enterprise  Logic"

@skwp @reverbdotcom #wcr14 I want to discover   relevant compromises
  rather than defend ideals

@skwp @reverbdotcom #wcr14

@skwp @reverbdotcom #wcr14 Over 115  Model Classes

@skwp @reverbdotcom #wcr14 Over 1000  Total Classes

@skwp @reverbdotcom #wcr14 Not great, but we have only three
chubby models

@skwp @reverbdotcom #wcr14 Are monoliths bad for business?

@skwp @reverbdotcom #wcr14 Quick Iterations Low Operational   Complexity Refactoring

Monolith Service Service Service Service Service Early 2013 - Startup
/ Proof of Concept

Monolith Service Service Service Service Service 2014 - Growth Phase

@skwp @reverbdotcom #wcr14 http://martinfowler.com/articles/distributed-objects- microservices.html “I'm wary of distribution and
  my default inclination is to prefer a monolithic design” “While small microservices are certainly simpler to reason about, I worry that this pushes complexity into the interconnections between services” “Refactoring becomes much harder when you have to do it across remote boundaries.”

@skwp @reverbdotcom #wcr14 Quick Iterations Low Operational   Complexity May
lead to a BBOM

@skwp @reverbdotcom #wcr14 Maintainable Monoliths Can Be Achieved

@skwp @reverbdotcom #wcr14 Product  400 LOC  ~150 LOC non-ActiveRecord Churn:
49 changes this year" Order  333 LOC  ~200 LOC non-ActiveRecord Churn: 36 changes this year User  338 LOC  ~200 LOC non-ActiveRecord Churn: 29 changes this year

CHURN Product Order User

@skwp @reverbdotcom #wcr14 Commonly used classes are hard to refactor

@skwp @reverbdotcom #wcr14 Stop   modifying   code!

@skwp @reverbdotcom #wcr14 Don’t put different rates of change together"
Kent Beck - Smalltalk Best Practice Patterns

@skwp @reverbdotcom #wcr14 Don’t put different rates of change together"
Kent Beck - Smalltalk Best Practice Patterns Data Model Business Logic

@skwp @reverbdotcom #wcr14 Separate   what the system is "
from what the system does" James Copelien & Trygve Reenskaug (Data, Context, Interaction)

@skwp @reverbdotcom #wcr14 Where does business logic go?

@skwp @reverbdotcom #wcr14 Controller 2005 ActiveRecord Mailers Services User

@skwp @reverbdotcom #wcr14 Console?" Rake task?" Background jobs?" API layer?"
Testing? What about…

@skwp @reverbdotcom #wcr14 Order Fat models?

@skwp @reverbdotcom #wcr14 Order Refund

@skwp @reverbdotcom #wcr14 Order Refund Ship

@skwp @reverbdotcom #wcr14 Order Refund Ship Check Fraud Risk

@skwp @reverbdotcom #wcr14 “Active Record is a good choice for
domain logic that isn't too complex, such as creates, reads, updates, and deletes” Martin Fowler

@skwp @reverbdotcom #wcr14 If Controller and Model are all you
have then   one has to be skinny and one has to be fat

@skwp @reverbdotcom #wcr14 Domain Layer skinny framework,   healthy business
logic," no fat anywhere http://joncairns.com/2013/04/fat-model- skinny-controller-is-a-load-of-rubbish/

Model Controller View The Rails Way The Way Active Record
Use Cases Grape API Controllers Cron Redis Rake HTTP Services Workers R Entities Roles DB Listeners Events

@skwp @reverbdotcom #wcr14 app/reverb for app speciﬁc

@skwp @reverbdotcom #wcr14 lib/reverb for Open Source / Generic

@skwp @reverbdotcom #wcr14 Reverb:: Namespace to avoid collisions with gems

@skwp @reverbdotcom #wcr14 This is a  marketplace! http://blog. 8thlight.com/uncle- bob/2011/09/30/
Screaming- Architecture.html

@skwp @reverbdotcom #wcr14 http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean- architecture.html

@skwp @reverbdotcom #wcr14 see also Hexagonal, Ports & Adapters, DCI

@skwp @reverbdotcom #wcr14 Clean   Enough   Architecture"

@skwp @reverbdotcom #wcr14 Choosing the right ﬁght

@skwp @reverbdotcom #wcr14 http://blog.8thlight.com/mike-ebert/2013/03/23/the- repository-pattern.html

@skwp @reverbdotcom #wcr14 http://blog.8thlight.com/mike-ebert/2013/03/23/the- repository-pattern.html (but you should still read
this)

@skwp @reverbdotcom #wcr14 User.where(…) User.active User.ﬁnd(1) This is easy to
replace with  something other than AR.   Repository not required. Don’t leak SQL outside of AR

@skwp @reverbdotcom #wcr14 Domain Logic in ActiveRecord and Controllers  leads
to Churn

@skwp @reverbdotcom #wcr14 Use Cases Reify complex business logic  into
classes

@skwp @reverbdotcom #wcr14 This is not" Rails

@skwp @reverbdotcom #wcr14 Explicitly Require Dependency http://myronmars.to/n/dev-blog/2012/12/5-reasons-to-avoid- bundler-require Invoke It

@skwp @reverbdotcom #wcr14 Code Reuse! Thin Shell

@skwp @reverbdotcom #wcr14 Stubby Happy Path

@skwp @reverbdotcom #wcr14 Testing conditionals and side effects has nothing
to do with Rails

@skwp @reverbdotcom #wcr14 Naming The hardest problem in computer science

@skwp @reverbdotcom #wcr14 OrderService

@skwp @reverbdotcom #wcr14 Order  Service

@skwp @reverbdotcom #wcr14 Order  Service NounService Grows Unbounded

@skwp @reverbdotcom #wcr14 Use verbs to narrow your scope

@skwp @reverbdotcom #wcr14 Order

@skwp @reverbdotcom #wcr14 Order ShipOrder

@skwp @reverbdotcom #wcr14 Order ShipOrder Cancel  Order

@skwp @reverbdotcom #wcr14 Order ShipOrder Cancel  Order Refund  Order

@skwp @reverbdotcom #wcr14 Order ShipOrder Cancel  Order Refund  Order Does
not  grow over time

@skwp @reverbdotcom #wcr14 ShipOrder Cancel  Order Refund  Order Don’t change"
once you write them

@skwp @reverbdotcom #wcr14 Ubiquitous Language

@skwp @reverbdotcom #wcr14 What is this?

@skwp @reverbdotcom #wcr14 Roles Add methods to objects on demand
in the context of a Use Case

@skwp @reverbdotcom #wcr14 Decorator

@skwp @reverbdotcom #wcr14 We added these methods

@skwp @reverbdotcom #wcr14 Methods related to each" other but loosely
related" to the parent concept" and used only in a few" Use Cases

@skwp @reverbdotcom #wcr14 Events Add behavior with listeners without modifying
code

@skwp @reverbdotcom #wcr14 Order ActiveRecord Callbacks Send Email

@skwp @reverbdotcom #wcr14 Order ActiveRecord Callbacks Send Email Call External
Service

@skwp @reverbdotcom #wcr14 Order ActiveRecord Callbacks Send Email Call External
Service Conditional  Callbacks

@skwp @reverbdotcom #wcr14 AR callbacks become more complex as the
system supports more use cases

@skwp @reverbdotcom #wcr14 Different use cases may trigger different events
even when working with the same model Instead

@skwp @reverbdotcom #wcr14 Add another listener to add behavior  The
core class doesn’t change

@skwp @reverbdotcom #wcr14 Global listeners for cross-cutting concerns  without littering
code Wisper::GlobalListeners.add(Reverb::Listeners::AnalyticsListener.new)"

@skwp @reverbdotcom #wcr14 Controller is a listener too

@skwp @reverbdotcom #wcr14 Policy Objects Reify complex business rules into
objects

@skwp @reverbdotcom #wcr14 Likely to change Unlikely to change

@skwp @reverbdotcom #wcr14 refactored for readability

@skwp @reverbdotcom #wcr14 Injectable, but has a default Simple code,
only need to test one path  for the imperative side effect" (sending an email)

@skwp @reverbdotcom #wcr14 Distillation Time

@skwp @reverbdotcom #wcr14 Language of codebase   reﬂects language of
business

@skwp @reverbdotcom #wcr14 Separate behaviors (what the system does) from
models (what the system is)

@skwp @reverbdotcom #wcr14 Rates of Change

@skwp @reverbdotcom #wcr14 Is this all Unicorns and Rainbows?

@skwp @reverbdotcom #wcr14 Sprawl?" Onboarding?" Naming?" Documentation?"

@skwp @reverbdotcom #wcr14 Active Record Use Cases Grape API Controllers
Cron Redis Rake HTTP Services Workers R Entities Roles DB Listeners Events Active Record Use Cases Grape API Controllers Cron Redis Rake HTTP Services Workers R Entities Roles DB Listeners Events

@skwp @reverbdotcom #wcr14 http://blog.mattwynne.net/category/hexagonal-rails/ http://clean-ruby.com/ Resources http://confreaks.com/videos/759-rubymidwest2011-keynote- architecture-the-lost-years http://blog.8thlight.com/uncle-bob/2011/09/30/Screaming- Architecture.html
http://www.artima.com/articles/dci_vision.html http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean- architecture.html https://speakerdeck.com/skwp

@skwp @reverbdotcom #wcr14 We Are Hiring Always" jobs.reverb.com Ruby, ElasticSearch,
DevOps, Designers, Android, and more! [email protected]

Domain Driven Rails

Domain Driven Rails

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