State machines

or

how to elegantly code changes to your models

Everybody has state

• some entries in the DB
• CRUD on them

Getting fancy

• callbacks: before_save, etc.
• why?

Have u ever seen the magic field?

• STATE
• or other variations...

Issues

• what values can state have => enum
• do I just update the state?
  • maybe u can put some callbacks
• when u update the state, u gotta update something else as well => find & replace
• can u update it with any possible value?
• the new guys comes in and doesn't know "conventions"

Alternative: state machines

• alias: finite state machine, finite automaton, etc.
• current state
• transitions

Hands on

https://github.com/state-machines/state_machines

Alternatives

state_machine

• exactly the same, but with some bugs
  • https://github.com/pluginaweek/state_machine/issues/251
• no longer maintained

aasm

• kinda the same
• one weird thing:
  • normal methods don't save
  • bang methods save
  • normal functionality is with exceptions
  • can be disabled on state machine level
• more fine grained transaction control

and others

• workflow
• ruote
• transitions

Gotchas

• not a silver bullet
• keep them simple (as simple as possible)
• can lead to hard to read code (same as with save callbacks)

Service Objects

• encapsulate everything about a transition
• controlled order of things
• write a lot of code
• gotta decide if it's worth it

?

Thanks