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# Trucker | ||
Trucker is a gem that helps migrate legacy data into a Rails app. | ||
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## Installation | ||
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### Install the trucker gem | ||
`sudo gem install trucker` | ||
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### Add the gem | ||
Add trucker to your <em>config.gem</em> block in `environment.rb`. | ||
```ruby | ||
config.gem "trucker" | ||
``` | ||
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### Generate the basic trucker files | ||
```bash | ||
script/generate truck | ||
``` | ||
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This will do the following things: | ||
- Add legacy adapter to database.yml | ||
- Add legacy base class | ||
- Add legacy sub classes for all existing models | ||
- Add app/models/legacy to autoload_paths in Rails Initializer config block | ||
- Generate sample migration task (using pluralized model names) | ||
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### Update the legacy database adapter in <em>database.yml</em> with your legacy database info | ||
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```yaml | ||
legacy: | ||
adapter: mysql | ||
encoding: utf8 | ||
database: app_legacy | ||
username: root | ||
password: | ||
``` | ||
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(By convention, we recommend naming your legacy database `APP_NAME_legacy`.) | ||
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### Database | ||
If the legacy database doesn't already exist, add it. | ||
```bash | ||
rake db:create:all | ||
``` | ||
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### Legacy data | ||
Import your legacy data into the legacy database. | ||
```bash | ||
mysql -u root app_legacy < old_database.sql | ||
``` | ||
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### `set_table_name` | ||
Update `set_table_name` in each of your legacy models as needed. | ||
```ruby | ||
class LegacyPost < LegacyBase | ||
set_table_name "LEGACY_TABLE_NAME_GOES_HERE" | ||
end | ||
``` | ||
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### Field mappings | ||
Update legacy model field mappings as needed. | ||
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```ruby | ||
class LegacyPost < LegacyBase | ||
set_table_name "YOUR LEGACY TABLE NAME GOES HERE" | ||
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def map | ||
{ | ||
:headline => self.title.squish, | ||
:body => self.long_text.squish | ||
} | ||
end | ||
end | ||
``` | ||
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New model attributes on the left side. | ||
Legacy model attributes on the right side. | ||
(aka :new_field => legacy_field) | ||
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### Need to tweak some data? | ||
Just add some core ruby methods or add a helper method. | ||
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```ruby | ||
class LegacyPost < LegacyBase | ||
set_table_name "YOUR LEGACY TABLE NAME GOES HERE" | ||
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def map | ||
{ | ||
:headline => self.title.squish.capitalize, # <= Added capitalize method | ||
:body => tweak_body(self.long_text.squish) # <= Added tweak_body method | ||
} | ||
end | ||
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# Insert helper methods as needed | ||
def tweak_body(body) | ||
body = body.gsub(/<br \//,"\n") # <= Convert break tags into normal line breaks | ||
body = body.gsub(/teh/, "the") # <= Fix common typos | ||
end | ||
end | ||
``` | ||
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### Start migrating! | ||
```bash | ||
rake db:migrate:posts | ||
``` | ||
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## Migration command line options | ||
Trucker supports a few command line options when migrating records: | ||
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```bash | ||
rake db:migrate:posts limit=100 (migrates 100 records) | ||
rake db:migrate:posts limit=100 offset=100 (migrates 100 records, but skip the first 100 records) | ||
``` | ||
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## Custom migration labels | ||
You can tweak the default migration output generated by Trucker by using the `:label` option. | ||
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```bash | ||
rake db:migrate:posts | ||
=> Migrating posts | ||
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rake db:migrate:posts, :label => "blog posts" | ||
=> Migrating blog posts | ||
``` | ||
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## Custom helpers | ||
Trucker is intended for migrating data from fairly simple web apps that started life on PHP, Perl, etc. So, if you're migrating data from an enterprise system, this may not be your best choice. | ||
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That said, if you need to pull off a complex migration for a model, you can use a custom helper method to override Trucker's default migrate method in your rake task. | ||
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```ruby | ||
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 | ||
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def pain_in_the_ass_migration | ||
# Custom code goes here | ||
end | ||
``` | ||
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Then just copy the migrate method from `lib/trucker.rb` and tweak accordingly. | ||
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As an example, here's a custom helper used to migrate join tables on a bunch of models. | ||
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```ruby | ||
namespace :db do | ||
namespace :migrate do | ||
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desc 'Migrates join tables' | ||
task :joins => :environment do | ||
migrate :joins, :helper => :migrate_joins | ||
end | ||
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end | ||
end | ||
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def migrate_joins | ||
puts "Migrating #{number_of_records || "all"} joins #{"after #{offset_for_records}" if offset_for_records}" | ||
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["chain", "firm", "function", "style", "website"].each do |model| | ||
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# Start migration | ||
puts "Migrating theaters_#{model.pluralize}" | ||
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# Delete existing joins | ||
ActiveRecord::Base.connection.execute("TRUNCATE table theaters_#{model.pluralize}") | ||
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# Tweak model ids and foreign keys to match model syntax | ||
if model == 'website' | ||
model_id = "url_id" | ||
send_foreign_key = "url_id".to_sym | ||
else | ||
model_id = "#{model}_id" | ||
send_foreign_key = "#{model}_id".to_sym | ||
end | ||
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# Create join object class | ||
join = Object.const_set("Theaters#{model.classify}", Class.new(ActiveRecord::Base)) | ||
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# Set model foreign key | ||
model_foreign_key = "#{model}_id".to_sym | ||
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# Migrate join (unless duplicate) | ||
"LegacyTheater#{model.classify}".constantize.find(:all, with(:order => model_id)).each do |record| | ||
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unless join.find(:first, :conditions => {:theater_id => record.theater_id, model_foreign_key => record.send(send_foreign_key)}) | ||
attributes = { | ||
model_foreign_key => record.send(send_foreign_key), | ||
:theater_id => record.theater_id | ||
} | ||
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# Check if theater chain is current | ||
attributes[:is_current] = {'Yes' => 1, 'No' => 0, '' => 0}[record.current] if model == 'chain' | ||
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# Migrate join | ||
join.create(attributes) | ||
end | ||
end | ||
end | ||
end | ||
``` | ||
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## Sample application | ||
Check out the [Trucker sample app](http://github.com/mokolabs/trucker_sample_app) for a working example of Trucker-based legacy data migration. | ||
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## Background | ||
Trucker is based on a migration technique using legacy models first pioneered by Dave Thomas: | ||
http://pragdave.blogs.pragprog.com/pragdave/2006/01/sharing_externa.html | ||
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## Note on patches/pull requests | ||
- Fork the project. | ||
- Make your feature addition or bug fix. | ||
- Add tests for it. This is important so we don't break a future version unintentionally. | ||
- Commit your changes, but do not mess with the rakefile, version, or history. | ||
(if you want to have your own version, that is fine but bump version in a commit by itself so we can ignore when we pull) | ||
- Send a pull request. Bonus points for topic branches. | ||
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## Contributors | ||
- Patrick Crowley / mokolabs | ||
- Rob Kaufman / notch8 | ||
- Jordan Fowler / TheBreeze | ||
- Roel Bondoc / roelbondoc | ||
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## Copyright | ||
Copyright (c) 2010 Patrick Crowley and Rob Kaufman. See [LICENSE](LICENSE) for details. |
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