data-migrations-split-fullname.rake

namespace :data do
  desc "Split the user's fullname into first and last names"
  task :split_fullname => :environment do
    User.reset_column_information
    User.find_each do |user|
      first_name, last_name = user.full_name.split ''
      
      user.first_name = first_name
      user.last_name  = last_name
      user.save!
    end
  end
end

data-migrations-step1.rb

class AddFirstNameAndLastNameToUsers < ActiveRecord::Migration
  def change
    add_column :users, :first_name, :string
    add_column :users, :last_name, :string
  end
end

data-migrations-step2.rb

class RemoveFullNameFromUsers < ActiveRecord::Migration
  def change
    remove_column :users, :full_name
  end
end