Question

I have an attribute in my model that is stored as text but interpreted as a rational. I have this method to handle that:

def start
  read_attribute(:start).to_r
end

When I set the start attribute to a new value, the start_was helper method returns a string, instead of a rational, but before I do so, it returns the correct value. Why?

Loading development environment (Rails 3.2.8)
1.9.3p194 :001 > d = Day.find(55)
  Day Load (8.7ms)  SELECT "days".* FROM "days" WHERE "days"."id" = ? LIMIT 1  [["id", 55]]
 => #<Day id: 55, date: "2012-03-30", start: "1/2", finish: "2/2", created_at: "2012-09-18 15:16:42", updated_at: "2012-09-19 08:20:41", day_year_id: 1> 

1.9.3p194 :002 > d.start_was
 => (1/2) 

1.9.3p194 :003 > d.start=0
 => 0 

1.9.3p194 :004 > d.start_was
 => "1/2" 

Answer 1

I think the reason is this method in ActiveModel (activemodel-3.2.8\lib\active_model\dirty.rb)

# Handle <tt>*_was</tt> for +method_missing+.
def attribute_was(attr)
  attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
end

As you see, if attribute was not actually changed it just calls its own getter, in your case hitting your start method which does the transformation. But if the attribute is actually changed, it reads its raw value from the changed_attributes storage.