I currently have something like this:

```
class Article

  # fields = [flag, something]

  after_create :update_flag

  def update_flag
    self.flag = 1 if something_changed?
  end
end

```

But it doesn't change the 'flag' field when I change the something field. I've saved the object. Still no changes.

```
a = Article.create(flag: 0, something: "content")
a.something = "different"
a.save

a.flag
> 0

```

Any ideas?