rails:db/seeds.rb

fugos.yml

fugos:
  -
    id: 1
    name: 'fugo'
  -
    id: 2
    name: 'fugofugo'

hoges.yml

hoges:
  -
    id: 1
    name: 'hoge'
  -
    id: 2
    name: 'hogehoge'

piyo_sample.sql

INSERT `piyos` VALUES(1, 'piyo');

seeds.rb

[Hoge, Fugo].each do |c|
  yml = File.read("#{Rails.root}/db/seeds/#{c.to_s.tableize}.yml")
  list = YAML.load(yml).symbolize_keys
  list[c.to_s.tableize.to_sym].each do |r|
    c.create do |t|
      r.each do |i, v|
        t.send "#{i}=", v
      end
    end
  end
end

if Rails.env.development?
  connection = ActiveRecord::Base.connection()
  [Piyo].each do |c|
    if c.count == 0
      open("#{Rails.root}/db/sql/#{c.to_s.tableize}_sample.sql") {|file|
        while sql = file.gets
          connection.execute sql
        end
      }
    end
  end
end