blackrat.org

One of the (many!) projects I’ve been working on required a ruby interface to a legacy database which contains existing state information in numeric form. I’ve been using aasm for other projects, and since the state is well defined, this seemed like a good opportunity to see if aasm would handle legacy data. I’ve already started to use ActiveRecord with it (this isn’t a rails app, but pure ruby), so I thought I’d have a quick spike to see what would happen.

A quick look at the source for aasm quickly revealed that it only uses strings for state information in the database, so a translation layer was required.

Since the column name containing the state information wasn’t state, I formulated a slightly cunning plan. Tell aasm that the column was called state, and create state and state= methods that would perform the database translation.

class TestStatus < ActiveRecord::Base
  aasm_column :state  #required to force aasm to call my state method rather than use its own internal column definition
  aasm_state :ok
  aasm_state :fail

  aasm_event :fail do
    transitions :to => :fail, :from=>[:ok]
  end

  aasm_event :ok do
     transitions :to => :ok, :from=>[:fail]
  end

  LEGACY_STATE={
    0=>:ok,
    1=>:fail
  }
  LEGACY_STATE_COLUMN=’ErrorState’

  def state
    LEGACY_STATE[read_attribute(LEGACY_STATE_COLUMN)]
  end

  def state=(value)
    write_attribute(LEGACY_STATE_COLUMN,LEGACY_STATE.invert[value])
  end