From legacy to DDD@andrzejkrzywda

Arkency

Did you write any code today?

Was it good code?

Are you proud of it?

Why?(do you think that surgeons are proud of their work?)

What is legacy code?Ruby is much more unified here than PHP

Any Rails code is legacy code

Legacy

• Frameworks

• monolithic

• no architecture

• no tests

DDD

Strategic vs Tactical DDD

Tactical DDD• entity

• value objects

• aggregate

• domain event

• services

• repositories

• factory

DDD-lite• app service

• domain service

• load aggregate from the repo

• do sth cool

• may use some value objects

• may trigger some domain events

• save aggregate (repo)

Strategic DDD

• bounded contexts

• context map

http://martinfowler.com/bliki/BoundedContext.html

Software House management tool

as microservices partially available

different persistencedata duplication

Context MapHR Project Management Finances

Invoicing

CRUD

DDD-lite

external SaaS

Communication

developer project client

How to get there from legacy?

BTW, There’s no such thing as the ultimate DDD codebase

Draw the Context Mapthe only thing to remember from this talk

Ongoing processNo time for 2-months rewrites

Peopleware the human factor

http://andrzejonsoftware.blogspot.com/2014/01/refactoring-human-factor.html

Escape from the CRUD verbsTalk more to the business people

Test coverage

#noregressions

when you’re a client you don’t like them too

Mutation testing is the real test coverage!

http://blog.arkency.com/2015/04/why-i-want-to-introduce-mutation-testing-to-the-rails-event-store-gem/

http://blog.arkency.com/2015/06/how-good-are-your-ruby-tests-testing-your-tests-with-mutant/

mutation testing php - humbug

https://github.com/padraic/humbug

Test units, not classes!http://andrzejonsoftware.blogspot.com/2015/02/tdding-unit-not-class.html

http://andrzejonsoftware.blogspot.com/2014/04/tdd-and-rails-what-makes-good-unit.html

http://blog.arkency.com/2014/09/unit-tests-vs-class-tests/

Escape from the framework ASAP

http://blog.arkency.com/2015/03/extract-a-service-object-in-any-framework/

Call application services from the framework

Active Record doesn’t make your code happy

AR is not DDD-lite-friendlyData Mapper is better here

Don’t just pass the params/hash everywherehttp://andrzejonsoftware.blogspot.com/2011/12/args-opts-params.html

Wrap your legacy contexts with the

application services layer

Use events to communicate between

bounded contextsrails_event_store

Separate reads/writes at the services layer

CQRS

Eliminate querying from BC to another

Push the data!

Keep the Bounded Contexts in-sync by publishing all the

important events

Easier testing when no dependency on other

system

Read modelsDenormalized data

Treat your frontend as a separate Bounded

Context

When in doubt, think in aggregates

Event sourcingbuild your aggregates from events

audit log for free(no, it’s not slow, but thanks for asking)

Distributed transactions are tricky

Easier setup of the project when it’s a smaller

pieceUseful when you’re maintaining many projects and need to bugfix them from time to time

https://laracasts.com/discuss/channels/general-discussion/folder-and-namespace-structure-with-ddd/replies/17753

Legacy -> DDD books

• red book, Vaughn Vernon

• blue book, Eric Evans

• Refactoring, Fowler

• Legacy code, Feathers

THANKS!(go draw your context maps now)