after_find callback broken after upgrade to rails3

Question

Grettings!

In an app that was working flawlessly in Rails 2.3.8 i have the following class method:

def self.encode(*attr_names)
  encoder = Encoder.new(attr_names)
  before_save encoder
  after_save encoder            
  after_find encoder
  define_method(:after_find) { } # defining here, since there's only alias in the Encoder class itself            
end

This method references the Encoder class. Here is it:

class Encoder
  include Encodings 

  def initialize(attrs_to_manage) # We're passed a list of attributes that should be stored encoded in the database
    @attrs_to_manage = attrs_to_manage
  end

  def before_save(model) # Before saving or updating, encode the attributes to their original encoding
    @attrs_to_manage.each do |field|
      model[field] = to_orig_encod(model[field])
    end
  end

  def after_save(model) # After saving, encode them back to utf8
    @attrs_to_manage.each do |field|
      model[field] = to_utf8(model[field])
    end
  end

  alias_method :after_find, :after_save # Do the same after finding an existing record
end

Before the upgrade to rails3 all the callbacks (before_save, after_save, after_find) worked fine. After the upgrade *before_save* and *after_save* still work, but *after_find* does not and I get the following deprecation warning in my log:

DEPRECATION WARNING: Base#after_find has been deprecated, please use Base.after_find :method instead

I'm uncertain how to change my code in order to re-enable the functionality of the after_find callback. I tried a few simple alternations with no success and the rails API documentation on this callback is very limited and without examples of implementation.

Any help appreciated, thanks in advance!

Edit:

Here's the solution:

Okay, so it seems that the problem was more subtle than it initially appeared. After additional testing I found out that in fact, as Jeppe pointed out, the after_find callback is working regardless of the deprecation warning, the "to_utf8" method was in fact suceesfully called and executed on the model attributes. The reason the result didn't match the expectations, was the "to_utf8" method itself. What it does is use the ruby module Iconv to convert strings from non-utf8 encoding like cp1251 for example to utf. This was done for the attributes of a model fetched with Active Record from a remote legacy database with non-utf encoding. However, as it turned out, unlike previous versions of rails, AR in rails 3 automagically and silently handles the conversion to ut8 of all objects, even those fetched from DB's that are not unicode. So essentially after the upgrade my code ended up re-converting to utf8 strings that were already converted to utf8 by AR and the result was a mess of gibberish characters. The problem was resolved by completely removing the after_find and after_save callbacks, since they are no longer needed in this case :)

Answer 1

Hi, I've tried to reproduce your problem, but I can only reproduce the deprecation warning, which you can get rid of by deleting your

define_method(:after_find) { }

statement.

All seems to work as expected besides that, both with and without the define_method statement.

My code:

class Testmodel < ActiveRecord::Base

  def self.encode(*attr_names)
    encoder = Encoder.new(attr_names)
    before_save encoder
    after_save encoder            
    after_find encoder
  end
end

class Encoder
  def initialize(attrs_to_manage) # We're passed a list of attributes that should be stored encoded in the database
    @attrs_to_manage = attrs_to_manage
  end

  def before_save(model) # Before saving or updating, encode the attributes to their original encoding
    @attrs_to_manage.each do |field|
      model[field] = to_orig_encod(model[field])
    end
  end

  def after_save(model) # After saving, encode them back to utf8
    @attrs_to_manage.each do |field|
      model[field] = to_utf8(model[field])
    end
  end

  alias_method :after_find, :after_save # Do the same after finding an existing record

  private
  def to_orig_encod(var)
    "foo"
  end

  def to_utf8(var)
    "bar"
  end
end

Console test:

ruby-1.9.2-p0 > Testmodel.create
 => #<Testmodel id: 3, name: nil, created_at: "2010-09-08 14:02:06", updated_at: "2010-09-08 14:02:06"> 
ruby-1.9.2-p0 > Testmodel.last
 => #<Testmodel id: 3, name: nil, created_at: "2010-09-08 14:02:06", updated_at: "2010-09-08 14:02:06"> 
ruby-1.9.2-p0 > Testmodel.encode('name')
 => [Testmodel(id: integer, name: string, created_at: datetime, updated_at: datetime)] 
ruby-1.9.2-p0 > Testmodel.last
 => #<Testmodel id: 3, name: "bar", created_at: "2010-09-08 14:02:06", updated_at: "2010-09-08 14:02:06"> 

I've been consulting the documentation at http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html to understand your question :-)