Migrating Legacy Data (Ruby Midwest)

Migrating Legacy Data

Patrick Crowley Rob Kaufman

(We’re from SD Ruby)

Let’s talk about migrating

Suck => Less Suck

PHP => Rails

Perl => Rails

Java => Rails

Rails => Rails

Migrating = pain

• Develop new site • Migrate data • Deploy new site

Migrate data

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

Sucks, right?

• Labor intensive • Error prone • One way trip

Trucker

Migrate legacy data (with less suck)

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

rake + legacy classes + migration helper

Let’s get started

sudo gem install trucker

conﬁg.gem “trucker”

script/generate truck

$ 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

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

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

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

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

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

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

Let’s do some migrating.

Don’t forget to import your legacy database!

$ 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)

$ 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)

$ 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)

Use helper method for custom migrations

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

What about?!?

Trucker helps you move.

But you still need to pack your stuff up.

Some other things to think about

Encoding issues

• MySQL issues: “ALTER TABLE mytable CONVERT TO CHARACTER SET utf8; • iconv

Java to the rescue?!?

JDBC Adapters vs ActiveRecord

• There are about 12 adapters in the wild for pure ActiveRecord • The ActiveRecord adapter for sqlserver runs on Win/Unix, but Unix setup is complicated • Text adapter does CSV, Tab, and other plain text formats

JDBC Adapters

ActiveRecord Tested:  MySQL  Derby  PostgreSQL  HSQLDB  Oracle  H2  Microsoft SQL  SQLite3 Server  Informix  DB2  FireBird

MSSQL – An Example

• Download MSSQL driver (Google for it, they move it around a lot) • Copy sqljdbc4.jar into RAILS_ROOT/lib • Add require 'lib/sqljdbc4.jar' at the top of your environment.rb or application.rb

conﬁg/database.yml legacy: adapter: jdbc username: USERNAME password: PASSWORD driver: com.microsoft.sqlserver.jdbc.SQLServerDriver jdbc: sqlserver://63.134.199.59:1433

Take it live

• Run in prod when you can • Run locally when you can't (Heroku, VPNs, etc)

Resources

• http://github.com/mokolabs/trucker • http://github.com/mokolabs/ trucker_sample_app • http://spkr8.com/t/3749

Special thanks to Dave Thomas

The End

Migrating Legacy Data (Ruby Midwest)

by Patrick Crowley on Jul 16, 2010

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