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.

Rule

What is it?

How do I get started?

Explain all that stuff.

Copyright