Setting a callback whose action depends on the previous state of the object

rubyonrails-talk
1

I've been reading about ActiveRecord::Callbacks and they're really cool. But I have a complex need I'm not sure they answer.

Let's say we have a User model. User has a #status attribute, which can be either "active", "closed" or "blocked".

I want to set a callback to perform an action if an "active" User has been blocked. So I need to know:

1. That the user has at first been in "active" status. 2. That his status has been set to "blocked".

I need to set the callback when someone tries to save him in this state, so to sum up:

I need to run some logic when someone updates a user.status from 'active' to 'blocked'.

Any idea how?

2

Thinking completely off the top of my head (e.g., none of this has actually been run), I'd say you could hook into the status writer and set a flag for later use in a before_save callback.

before_save :handle_newly_blocked

def status=(new_status)    if self.status == 'active' && new_status == 'blocked'      @newly_blocked = true    end    write_attribute(:status, new_status) end

def handle_newly_blocked    if @newly_blocked      # .. handle it ..    end end

-Rob

Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com

3

Although your example is a simple state machine, I am a big fan of acts_as_state_machine.

http://lunchroom.lunchboxsoftware.com/2006/1/21/acts-as-state-machine

Jodi

4

Sorry for the late response, but I couldn't resist telling you to look at the acts_as_state_machine plugin. It lets you program transition logic like you're describing declaratively.