Rule¶ ↑

What is it?¶ ↑

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

How do I get started?¶ ↑

1. Add it to your gemfile.

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

2. Add a “state” column and this code to your model:

   rule_engine MyAwesomeRuleEngine
   

3. 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

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

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

5. 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 © 2011 Burke Libbey / Innovatis. MIT License.