ActiveRecord observers can't be used for "before" callbacks

Gosh, I ran into the same thing today.

As long as you don't care about the return value this hax seems to work for now

ActiveRecord::Observer.class_eval do
  def add_observer!(klass)
    super
    self.class.observed_methods.each do |method|
      callback = :"_notify_observers_for_#{method}"
      if (klass.instance_methods & [callback, callback.to_s]).empty?
        klass.class_eval "def #{callback}; notify_observers(:#{method}); true; end"
        klass.send(method, callback)
      end
    end
  end
end

That's the exact monkeypatch I did in Radiant

Taken a stab at fixing this. This patch includes changes from the above patch. Detailed explanation of the changes in commit messages, but here is the last (and most important):

improve how ActiveRecord::Observer defines callbacks on observed models

Instead of using a single notify_observers call for every callback type, each observer now registers a unique callback for itself. Example:

before_save :_notify_user_observer_for_before_save

def _notify_user_observer_for_before_save
  observer.update(:before_save, self)
end

Benefit: "before" callbacks halt when observer.update returns false. This way, ActiveRecord observers can prevent records from saving.