rule

= Rule

== What is it?

Rule is a state machine / rule engine. It does things.

== How do I get started?

• Add it to your gemfile.

  gem "rule", :git => "https://github.com/innovatis/rule"

• Add a "state" column and this code to your model:

  rule_engine MyAwesomeRuleEngine

• create a file at app/rule_engines/my_awesome_rule_engine.rb

  class MyAwesomeRuleEngine < Rule::Engine::Base

  state :new state :ongoing state :closed

  initial_state :new

  terminal_state :closed

  transition :new, :ongoing validate IsInProgressRule end

  transition :ongoing, :closed assert_presence_of object.closed_at, "Closed At" end

  end

• Create a file at app/rules/is_in_progress_rule.rb

  class IsInProgressRule < Rule::Base def validate @object.in_progress.present? end end

• Set your application up to run the rules.

  wherever it makes sense...

  my_object.run_rules # advances state as far as possible and automatically saves

== Explain all that stuff.

Okay.

The Rule::Engine::Base subclass defines states and transitions. Each transition block contains a number of assertions and an optional priority. If any of the assertions does not pass, the state will not follow this transition. The priority decides which transition to use in the case of two possible transitions out of the current state both being valid. Use it by specifying "priority :high" or "priority :low" in the transition block.

It often makes sense to bundle a group of assertions into a Rule class. These are defined in app/rules, and have a validate method containing assertions. In the future, rules will also have callbacks that fire when the state is advanced through a transition including that rule.

If this didn't answer your questions, throw things at Burke until he explains.

== Copyright

Copyright (c) 2011 Burke Libbey / Innovatis. MIT License.