DATAMAPPER AUTOMIGRATE VS AUTOUPGRADE

example.rb

require 'dm-core'
require 'dm-migrations'

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'mysql://localhost/test')

class Person
  include DataMapper::Resource
  property :id,   Serial
  property :name, String, :required => true
end

DataMapper.auto_migrate!

# ~ (0.015754) SET sql_auto_is_null = 0
# ~ (0.000335) SET SESSION sql_mode = 'ANSI,NO_BACKSLASH_ESCAPES,NO_DIR_IN_CREATE,NO_ENGINE_SUBSTITUTION,NO_UNSIGNED_SUBTRACTION,TRADITIONAL'
# ~ (0.283290) DROP TABLE IF EXISTS `people`
# ~ (0.029274) SHOW TABLES LIKE 'people'
# ~ (0.000103) SET sql_auto_is_null = 0
# ~ (0.000111) SET SESSION sql_mode = 'ANSI,NO_BACKSLASH_ESCAPES,NO_DIR_IN_CREATE,NO_ENGINE_SUBSTITUTION,NO_UNSIGNED_SUBTRACTION,TRADITIONAL'
# ~ (0.000932) SHOW VARIABLES LIKE 'character_set_connection'
# ~ (0.000393) SHOW VARIABLES LIKE 'collation_connection'
# ~ (0.080191) CREATE TABLE `people` (`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `name` VARCHAR(50) NOT NULL, PRIMARY KEY(`id`)) ENGINE = InnoDB CHARACTER SET utf8 COLLATE utf8_general_ci
# => #<DataMapper::DescendantSet:0x101379a68 @descendants=[Person]>
class Person
   property :hobby, String
end

DataMapper.auto_upgrade!

# ~ (0.000612) SHOW TABLES LIKE 'people'
# ~ (0.000079) SET sql_auto_is_null = 0
# ~ (0.000081) SET SESSION sql_mode = 'ANSI,NO_BACKSLASH_ESCAPES,NO_DIR_IN_CREATE,NO_ENGINE_SUBSTITUTION,NO_UNSIGNED_SUBTRACTION,TRADITIONAL'
# ~ (1.794475) SHOW COLUMNS FROM `people` LIKE 'id'
# ~ (0.001412) SHOW COLUMNS FROM `people` LIKE 'name'
# ~ (0.001121) SHOW COLUMNS FROM `people` LIKE 'hobby'
# ~ (0.153989) ALTER TABLE `people` ADD COLUMN `hobby` VARCHAR(50)
# => #<DataMapper::DescendantSet:0x101379a68 @descendants=[Person]>