Question

I am using Aaron Pfeifer’s state_machine gem in my Rails3 app — it’s (still) nifty.

I have a event whose outcome isn’t known until it has been processed, and I would like to set the following state based on the outcome. The ‘obvious’ approach shown here doesn’t work: it raises an ArgumentError: :picked_many is not a known state value error.

What’s the right way to set the state based on the outcome of an event? (Or am I just thinking about this wrong?)

class MyModel < ActiveRecord::Base 
  state_machine :initial => :top do 
    event :pickanumber do
      transition any => any
    end 
    state :picked_zero 
    state :picked_one 
    state :picked_many 
  end 
  def pickanumber(n) 
    self.state = case n 
                 when 0 then :picked_zero 
                 when 1 then :picked_one 
                 else :picked_many 
                 end 
    super
  end 
end 

and a sample run:

> m = MyModel.create 
=> #<MyModel id: 26, state: "top", ...>
> m.pickanumber(2) 
ArgumentError: :picked_many is not a known state value

Answer 1

State is internally stored as a string and not symbol.

This should work…

def pickanumber(n)
    self.state = case n
                 when 0 then "picked_zero"
                 when 1 then "picked_one"
                 else "picked_many"
                 end
    super
end