Migrating Legacy Data
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This talk describes a nice technique for migrating legacy data into a Rails app. Code samples are here: http://github.com/mokolabs/legacy/tree/master
![/app/models/legacy_base.rb
class LegacyBase < ActiveRecord::Base
self.abstract_class = true
establish_connection quot;legacyquot;
def migrate
new_record = eval(quot;#{self.class}quot;.gsub(/Legacy/,'')).new(map)
new_record[:id] = self.id
new_record.save
end
end](https://image.slidesharecdn.com/migrating-1233951402854617-2/85/Migrating-Legacy-Data-15-320.jpg)
![/lib/migration_helper.rb
def migrate(name, options={})
# Grab custom entity label if present
label = options.delete(:label) if options[:label]
unless options[:helper]
model = name.to_s.singularize.capitalize
model.constantize.delete_all
puts quot;Migrating #{number_of_records || quot;allquot;} #{label || name} #{quot;after #{offset_for_records}quot; if
offset_for_records}quot;
quot;Legacy#{model}quot;.constantize.find(:all, with(options)).each do |record|
record.migrate
end
else
eval options[:helper].to_s
end
end
def with(options={})
{:limit => number_of_records, :offset => offset_for_records}.merge(options)
end
def number_of_records
nil || ENV['limit'].to_i if ENV['limit'].to_i > 0
end
def offset_for_records
nil || ENV['offset'].to_i if ENV['offset'].to_i > 0
end](https://image.slidesharecdn.com/migrating-1233951402854617-2/85/Migrating-Legacy-Data-18-320.jpg)
![/lib/tasks/migrate.rake
require 'migration_helper'
namespace :db do
namespace :migrate do
desc 'Migrates legacy content'
task :legacy => [quot;architectsquot;, quot;stylesquot;]
desc 'Migrates architects'
task :architects => :environment do
migrate :architects
end
desc 'Migrates theaters'
task :theaters => :environment do
migrate :theaters
end
end
end](https://image.slidesharecdn.com/migrating-1233951402854617-2/85/Migrating-Legacy-Data-20-320.jpg)
Migrating Legacy Data
- 1. Patrick Crowley the.railsi.st
- 5. How do you migrate your old data?
- 7. Dump old database
- 8. Dump old database Massage text with TextMate, BBEdit, grep, etc.
- 9. Dump old database Massage text with TextMate, BBEdit, grep, etc. Eventually give up
- 10. Dump old database Massage text with TextMate, BBEdit, grep, etc. Eventually give up Import into new database
- 11. Heres a better way.
- 12. Step 1: Add new db adapter
- 13. /con鍖g/database.yml development: adapter: mysql encoding: utf8 database: cinema_development username: root password: ... legacy: adapter: mysql encoding: utf8 database: cinema_legacy username: root password:
- 14. Step 2: Add Legacy models
- 15. /app/models/legacy_base.rb class LegacyBase < ActiveRecord::Base self.abstract_class = true establish_connection quot;legacyquot; def migrate new_record = eval(quot;#{self.class}quot;.gsub(/Legacy/,'')).new(map) new_record[:id] = self.id new_record.save end end
- 16. /app/models/legacy_architect.rb class LegacyArchitect < LegacyBase set_table_name quot;architectquot; def map { :first_name => self.name_first, :last_name => self.name_last, :description => self.desc_long } end end
- 17. Step 3: Add Migration helper
- 18. /lib/migration_helper.rb def migrate(name, options={}) # Grab custom entity label if present label = options.delete(:label) if options[:label] unless options[:helper] model = name.to_s.singularize.capitalize model.constantize.delete_all puts quot;Migrating #{number_of_records || quot;allquot;} #{label || name} #{quot;after #{offset_for_records}quot; if offset_for_records}quot; quot;Legacy#{model}quot;.constantize.find(:all, with(options)).each do |record| record.migrate end else eval options[:helper].to_s end end def with(options={}) {:limit => number_of_records, :offset => offset_for_records}.merge(options) end def number_of_records nil || ENV['limit'].to_i if ENV['limit'].to_i > 0 end def offset_for_records nil || ENV['offset'].to_i if ENV['offset'].to_i > 0 end
- 19. Step 4: Add Rake task
- 20. /lib/tasks/migrate.rake require 'migration_helper' namespace :db do namespace :migrate do desc 'Migrates legacy content' task :legacy => [quot;architectsquot;, quot;stylesquot;] desc 'Migrates architects' task :architects => :environment do migrate :architects end desc 'Migrates theaters' task :theaters => :environment do migrate :theaters end end end
- 22. Demo
- 24. Special thanks
- 25. Questions?
- 26. The End