rails3_tableless_model.rb

class User < ActiveRecord::Base
  class_attribute :columns
  def self.columns
    @columns ||= [];
  end

  def self.column(name, sql_type = nil, default = nil, null = true)
    columns << ActiveRecord::ConnectionAdapters::Column.new(
      name.to_s,
      default,
      sql_type.to_s,
      null
    )
  end

  column :name, :text
  column :country_id, :integer
  belongs_to :country
end