Conditional state transitions with AASM

Also part of the same state machine I wrote about in "Chaining state transitions with Acts As State Machine (aasm)" required two different types of behavior for a state transition.

The task reviewer state was optional and would be triggered only if selected. I represented that state as a "use_reviewer" boolean column in the object. If use_reviewer == true, then the object transitions from task_created to "to_reviewer", otherwise it needed to transition to "to_writer"

The solution to this is rather straight forward. Use the :guard option in the aasm_event definition.

Here's the code:

aasm_event :created do
transitions :to => :to_reviewer, :from => [:task_created], :guard => Proc.new {|p| p.use_reviewer == true }
transitions :to => :to_writer, :from => [:task_created]
end

The event causes the object to transition to the "to_reviewer" state if the objects "use_reviewer" is true, otherwise it transitions to "to_writer". Here's the code evidence from script/console:

>> a = Assignment.new
=> (Assignment object)
>> a.use_reviewer = true
=> true
>> a.save
=> true
>> a.created!
=> true
>> a.aasm_current_state
=> :to_reviewer

Now we start over:
>> a = Assignment.new
=>(Assignment object)
>> a.save
=> true
>> a.created!
=> true
>> a.aasm_current_state
=> :to_writer