How to best represent a field that uses multiple inputs with activerecord

account.rb

# The problem I have is that I've got a sort_code field in the database, and I want to keep that as one field
# BUT I want users to edit it in the form using 3 different fields.

# My initial solution was to use virtual attributes and divide it this way. 
# Can you think of a better way?

class Account < ActiveRecord::Base

  def sort_code_one
    sort_code[0..1]
  end

  def sort_code_one=(value)
    sort_code[0] = value[0].to_s
    sort_code[1] = value[1].to_s
  end

  def sort_code_two
    sort_code[2..3]
  end

  def sort_code_two=(value)
    sort_code[2] = value[0].to_s
    sort_code[3] = value[1].to_s
  end

  def sort_code_three
    sort_code[4..5]
  end

  def sort_code_three=(value)
    sort_code[4] = value[0].to_s
    sort_code[5] = value[1].to_s
  end
end

# And in the form:

<%= form_for @account do |f| %>
  <%= f.label :sort_code %>
  <%= f.text_field sort_code_one %>
  <%= f.text_field sort_code_two %>
  <%= f.text_field sort_code_three %>
<% end %>

Rails’ multiparameter attribute assignment should take care of this (or at least it’s a convention to follow):
https://github.com/rails/rails/blob/d90b4e2/activerecord/lib/active_record/base.rb#L1811

I was going to fork this and do something where you have a sort_code_parts method that takes a hash, but I realised building the form wouldn't be as easy as f.text_field. I suppose it's about where you want to have the messy code, in the model as you have, or in a helper as I would.

@h-lame Actually, that's a good point. This code is purely for displaying the sort code, and has no business being in the model. A helper makes more sense