SeedFile, a helper for doing database setup in a Rails 3 app

seed_file.rb

# Helper class for importing files with records to the database.
class SeedFile
  def self.import(path)
    new(path).import
  end

  attr_reader :path

  def initialize(path)
    @path = Pathname(path)
  end

  # Imports this seed file to its corresponding table in the database.
  def import
    open do |io|
      case format
      when :yml, :yaml
        import_yaml(io)
      when :json
        import_json(io)
      end
    end

    return true
  end

  # Returns the format of this seed file as a symbol (e.g. :yaml or :json).
  def format
    (gzip?? path.basename(path.extname) : path).extname[1..-1].downcase.to_sym
  end

  # Returns true if the seed file is gzipped.
  def gzip?
    path.extname == '.gz'
  end

  private

  def open(&block)
    if gzip?
      IO.popen("gunzip -c #{path.realpath}", &block)
    else
      path.open(&block)
    end
  end

  # Gets the ActiveRecord::Base subclass for this seed file.
  def klass
    @klass ||= path.          # #<Pathname:db/seeds/countries.yml>
               basename.      # #<Pathname:countries.yml>
               to_s.          # "countries.yml"
               split('.').    # ["countries", "yml"]
               first.         # "countries"
               classify.      # "Countries"
               singularize.   # "Country"
               constantize    # Country
  end

  # Imports a YAML array of records, i.e.:
  #
  #   ---
  #   - name: Jeff
  #     born_on: 1983-10-19
  #   - name: Brad
  #     born_on: 1972-02-06
  def import_yaml(io)
    require 'yaml' unless defined?(YAML)
    YAML.load(io).each {|data| import_record data }
  end

  # Imports JSON structures one line at a time, i.e.:
  #
  #   {"name":"Jeff","born_on":"1983-10-19"}
  #   {"name":"Brad","born_on":"1972-02-06"}
  def import_json(io)
    require 'active_support/json' unless defined?(ActiveSupport::JSON)
    while line = io.gets
      import_record ActiveSupport::JSON.decode(line.chomp)
    end
  end

  def import_record(attributes)
    klass.new.tap do |record|
      # bypass attr_accessible / attr_protected
      attributes.each do |key, value|
        record[key] = value
      end
      # bypass validations
      record.save :validate => false
    end
  end
end

seeds.rb

# This is an example seeds.rb file from a Rails 3 project. If you put seed_file.rb in lib,
# then put .yml & .json in db/seeds, then you can just use this to import them:

Rails.root.join('db/seeds').children.each do |child|
  begin
    puts "** Importing #{child.basename}"
    SeedFile.import(child)
  rescue NameError => e
    abort "!! #{e}"
  end
end