Rails error handling with AASM state machine

Question

I'm using the rubyist-aasm state machine for handling the different states in my Event object (event initialized, event discussed, event published, etc.). I added guards to prevent state changes when certain conditions aren't met. This all works fine but it doesn't show any errors when a state change was rejected by the guard. Any idea how I can see the state didn't change? I could check the states manually but it sounds like an ugly solution. ``` aasm_state :firststate aasm_state :secondstate aasm_event :approve do transitions :to => :secondstate, :from => [:firststate], :guard => :has_a_price? end def has_a_price? self.price.present? end ```

Accepted Answer

With SimpleStateMachine you can guard state transitions by adding errors:

```
def approve
  errors.add(:price, 'Invalid') if price.blank?
end
event :approve, :firststate => :secondstate
```

Although in this case the price being present isn't related to the event so it would be enough to do:

```
validates_presence_of :price, :if => "self.second_state?"
event :approve, :firststate => :secondstate
```

Rails error handling with AASM state machine

Solution

Problem