The document discusses migrating legacy data from one application to another using the Trucker gem. It provides an overview of the typical manual and error-prone migration process and introduces Trucker as a way to migrate data from day one and improve it over time. The document then demonstrates how to generate a Trucker migration, define legacy model classes and mappings, run migrations in batches, and use custom helper methods.

1. Trucker

2. Let’s talk about
migrating

3. Suck => Less Suck

4. PHP => Rails

5. Perl => Rails

6. Java => Rails

7. Rails => Rails

8. Migrating = pain

10. • Develop new site

11. •Develop new site
• Migrate data

12. •Develop new site
• Migrate data
• Deploy new site

13. Migrate data

15. • Dump database

16. •Dump database
• Drop some tables

17. •Dump database
• Drop some tables
• Rename attributes

18. •Dump database
• Drop some tables
• Rename attributes
• Tweak data by hand

19. •Dump database
• Drop some tables
• Rename attributes
• Tweak data by hand
• Import data into new app

20. •Dump database
• Drop some tables
• Rename attributes
• Tweak data by hand
• Import data into new app
• Pray things are okay

21. Sucks, right?

23. • Labor intensive

24. •Labor intensive
• Error prone

25. •Labor intensive
• Error prone
• One way trip

26. Trucker

27. Migrate legacy data
(with less suck)

29. • Migrate data from day one

30. •Migrate data from day one
• Improve data over time

31. •Migrate data from day one
• Improve data over time
• Launch with confidence

32. rake +
legacy classes +
migration helper

33. Let’s get started

34. sudo gem install trucker

35. config.gem “trucker”

36. script/generate truck

37. $ script/generate truck
create app/models/legacy
create app/models/legacy/legacy_base.rb
exists lib/tasks
create lib/tasks/legacy.rake
insert added legacy adapter to end of database.yml
insert added new load path to environment.rb

38. config/environment.rb
Rails::Initializer.run do |config|
config.load_paths += %W( #{RAILS_ROOT}/app/
models/legacy )
end

39. config/database.yml
legacy:
adapter: mysql
encoding: utf8
database: trucker_legacy
username: root
password:

40. app/models/legacy/legacy_base.rb
class LegacyBase < ActiveRecord::Base
self.abstract_class = true
establish_connection "legacy"
def migrate
new_record = self.class.to_s.gsub(/
Legacy/,'::').constantize.new(map)
new_record[:id] = self.id
new_record.save
end

41. app/models/legacy/legacy_post.rb
class LegacyPost < LegacyBase
set_table_name "blog_posts"
def map
{
:name => self.headline.squish,
:body => self.body.squish
}
end
end

42. app/models/legacy/legacy_post.rb
class LegacyPost < LegacyBase
set_table_name "blog_posts"
def map
{
:name => tweak(self.headline.squish),
:body => self.body.squish
}
end
def tweak(name)
name.capitalize.gsub(/teh/, "the")
end

43. lib/tasks/legacy.rake
namespace :db do
namespace :migrate do
desc 'Migrates posts'
task :posts => :environment do
Trucker.migrate :posts
end
end
end

44. Let’s do some migrating.

45. Don’t forget to import
your legacy database!

46. $ rake db:migrate:posts
Migrating all posts (1/10)
Migrating all posts (2/10)
Migrating all posts (3/10)
Migrating all posts (4/10)
Migrating all posts (5/10)
Migrating all posts (6/10)
Migrating all posts (7/10)
Migrating all posts (8/10)
Migrating all posts (9/10)
Migrating all posts (10/10)

47. $ rake db:migrate:posts limit=5
Migrating 5 posts (1/10)
Migrating 5 posts (2/10)
Migrating 5 posts (3/10)
Migrating 5 posts (4/10)
Migrating 5 posts (5/10)

48. $ rake db:migrate:posts limit=5 offset=5
Migrating 5 posts after 5 (6/10)
Migrating 5 posts after 5 (7/10)
Migrating 5 posts after 5 (8/10)
Migrating 5 posts after 5 (9/10)
Migrating 5 posts after 5 (10/10)

49. $ rake db:migrate:posts limit=5 offset=5 delete_all=true
Migrating 5 posts after 5 (6/10)
Migrating 5 posts after 5 (7/10)
Migrating 5 posts after 5 (8/10)
Migrating 5 posts after 5 (9/10)
Migrating 5 posts after 5 (10/10)

50. DEMO

51. Use helper method for
custom migrations

52. namespace :db do
namespace :migrate do
desc 'Migrate pain_in_the_ass model'
task :pain_in_the_ass => :environment do
Trucker.migrate :pain_in_the_ass, :helper => pain_in_the_ass_migration
end
end
end
def pain_in_the_ass_migration
# Custom code goes here
end

53. What about?!?

54. Trucker helps you move.

55. But you still need to
pack your stuff up.

56. Resources

58. • http://github.com/mokolabs/trucker

59. • http://github.com/mokolabs/trucker
• http://github.com/mokolabs/
trucker_sample_app

60. Special thanks
to Dave Thomas

61. The End