From: "Marcin Rzeźnicki" <marcin.rzeznicki@...>
Date: 2013-04-13T21:32:13+09:00
Subject: [ActiveRecord] Attribute aliasing is driving me nuts :-)

Hi folks!
First of all: This is crosspost from Rails mailing list, I can't seem
to find answer there, so I thought I could as well try here. Having
said that, here is the original post:

Quick question about alias_attribute in context of legacy database. I am
on
AR 3.2.11. I got very weird, but easy to follow, naming scheme to deal
with. That is - every attribute is suffixed by '_'. I thought I dealt
with
that cleverly, that is, I introduced common 'abstract' base class for my
models:

     class PersistentObject < ActiveRecord::Base
          self.abstract_class = true

          #...

          def self.define_attribute_methods
            super
            attribute_names.each do |old_name|
              next if old_name == primary_key
              if old_name == locking_column
                alias_attribute 'version', old_name
              else
                new_name = old_name.chomp('_')
                new_name.downcase!
                alias_attribute new_name, old_name if new_name !=
old_name
              end
            end
          end
        end

Basic things do work, I can refer to something called 'FLOWER_' by
model.flower, also some validators work correctly, eg. this one is fine:

validates_length_of :name, :category, maximum: 255, allow_nil: true

But, as always, not all that glitters is gold. Some things fail
miserably
eg. :

validates_uniqueness_of :name, scope: :category

throws weird errors about nil not responding to a method etc. That
escaped
my logic until I debugged what was really going on ( (I'll get back to
this
later). You can fix that by using:

validates_uniqueness_of :NAME_, scope: :CATEGORY_

Ugly, but works. Same things goes for dynamic finders. #find_by_name
refuses to cooperate  #find_by_NAME_ is fine. I read in various places
about this problem and, honestly, didn't like what I found out
(euphemism
for - I found that mightily stupid :-)). Then I started figuring this
out
by myself trying to judge what it takes to make at least unique
validator
work.  After a bit of debugging I nailed that down to:
#activerecord/validations/uniqueness.rb:56
#build_relation
column = klass.columns_hash[attribute.to_s]

Needles to say columns_hash cares nothing about my aliases and happily
tries to procede with nil. Ok, so I modified my aliasing method to
actually
pack the stuff I needed into columns_hash, luckily at the point of
aliasing
columns've already been created so I could just put copies under
respective
new keys. That let me go past this issue but when I saw generated query
I
was stunned - it used wrong names in all the places. Madness. I gave up.
So, my question is: maybe you know someone who has taken on this issue
and
released a solution? Or maybe there are plans to fix this on AR level?
Or,
the most welcome possibility, maybe this is dead simple to fix :-) I
appreciate all the answers, thanks in advance.