Directly access/validate underlying ActiveRecord model association record values

I recently ran into a situation where proper table normalization in my design left me with a clunky UI implementation, and no change logging. I also needed a way to directly access underlying (has-one) records for an object, through it's own accessor (think batch import). In the past, for chang logging, I've used ActiveRecord observers, or used an existing library such as Paper Trail, but I wanted this to fit into my scoped non-library dependent design and allow easy access to the underlying has-one records.

I've altered the exact implementation, the below is just an example:

Tables (users, phones) - sqlite3 syntax:

• create table users (id integer primary key, first_name text, last_name text, created_at text, updated_at text, deleted_at text);


• create table phones (id integer primary key, user_id integer, phone_type text, number text, created_at text, updated_at text, deleted_at text);

Models (User, Phone):

class User < ActiveRecord::Base
  default_scope :conditions => { :deleted_at => nil }
  has_many :phones
  
  validates_presence_of [ :first_name, :last_name, :cell_phone ]
  validates_format_of :cell_phone, :with => /\d{3}-\d{3}-\d{4}/, :if => Proc.new {|o| !o.errors.on( :cell_phone ) }

  accepts_nested_attributes_for :phones
  
  def cell_phone
    @cell_phone || ( !self.phones.empty? ? self.phones.cell.first.number : nil )
  end

  def cell_phone=( value )
    @cell_phone = value
    if self.phones.cell.empty? then
      self.phones.build( :phone_type => 'cell', :number => value )
    else
      phone = self.phones.cell.first
      self.phones_attributes = [ { :id => phone.id, :number => value } ]
    end
  end  
  
  def destroy
    self.update_attribute( :deleted_at, Time.now )    
  end  
end


class Phone < ActiveRecord::Base
  default_scope :conditions => { :deleted_at => nil }
  named_scope :cell, :conditions => { :phone_type => 'cell' }
  
  belongs_to :user
  
  def destroy
    self.update_attribute( :deleted_at, Time.now )    
  end  
end

OK ... but what's it do?

• Validation that plays nice with form view helpers:
  
  
  >> u = User.new( :first_name => 'Noel', :last_name => 'Geren' )
  => #
  >> u.valid?
  => false
  >> u.errors.full_messages.join(", ")
  => "Cell phone can't be blank"
  


• Direct access to underlying has-one (cell phone record):
  
  
  u = User.new( :first_name => 'Noel', :last_name => 'Geren' )
  => #
  >> u.cell_phone = '123-123-1234'
  => "123-123-1234"
  >> u.cell_phone
  => "123-123-1234"