Presentation on replacing ActiveRecord with DataMapper in a Ruby on Rails application. Blog posting with info: http://degenportnoy.blogspot.com/2008/12/replacing-activerecord-with-datamapper.html Source: http://github.com/PeterDP/ar2dm

1. Replacing ActiveRecord
with DataMapper
in Ruby on Rails
Peter Degen-Portnoy
November 25, 2008

2. DataMapper is an ORM

3. A lot like ActiveRecord
●
DB Adapters
●
Migrations
●
Associations
●
One to one
●
One to many
●
Many to many
●
Many to one

4. Application Rails Merb
ORM DataMapper
Adaptors DO.rb YAML IMAP
Storage

5. Most often used with Merb
...but not exclusively

6. DataMapper Goodness
●
Identity Map
●
Mappings in Model
●
Multiple Repositories
●
Lazy Loads of Large Lumps
●
Strategic Eager Loading

7. Identity Map
●
One object for one row
●
Reduces hits to database
●
Exists during Identity Map Session

8. Mapping in Model
●
Persist any class
●
Independent data store evolution
●
Connect to multiple databases
●
DM issues updates or creates only for what
it knows

9. Multiple Repositories
●
Nested YAML structure
●
Override target table names
●
Specify connection per class or even call

10. Lazy Loading
●
Reduces load of large columns
●
Text
●
Blobs
●
Graphics
●
Specify which columns lazy load
●
Lazy loads happen together; only 1 more call
●
Can be grouped

11. Strategic Eager Loading
●
One call per child
●
Eliminates n+1 calls for associations

12. Way faster than ActiveRecord

13. 10,000 records fetched w/ Active Record
Average: 1.3429 seconds

14. 10,000 records fetched w/ DataMapper
Average: 0.0002 seconds

15. 1.3429 seconds compared to 0.0002 seconds

16. 0.0150% as much time

17. To Fetch 1,000 Records
ActiveRecord Over 204,000 calls
DataMapper Under 7,000 calls

18. Replacing ActiveRecord with DataMapper
the part for which you have been waiting

19. Demo Applications
●
One application to test ActiveRecord
●
One application to test DataMapper
●
Each create same data structure:
●
script/generate model book amount:float
date:date name:string description:text
--skip-timestamps
●
Create 1000 records
●
Profile & Benchmark

20. Gems You Need
●
data_mapper
●
do_mysql (or do_postgres or do_sqlite3)
●
dm-core
●
fastthread
●
json
●
rspec

21. Edit config/environment.rb
●
config.frameworks -= [ :active_record ]
●
config.gem “do_mysql”
●
config.gem “dm-core”
●
config.gem “dm-migrations”
Make sure your gems are up to date by
running “sudo rake gems:install”

22. Configure database.yml
development: &defaults
:adapter: mysql
:database: dm2_dev
:user: root
:password: mysql
:socket: /var/run/mysqld/mysqld.sock
:host: localhost
test:
<<: *default
:database: dm2_test
production:
<<: *default
:database: dm2_prod

23. Create
config/initializers/datamapper.rb
require quot;dm-corequot;
hash = YAML.load(File.new(Rails.root + quot;/config/database.ymlquot;))
DataMapper.setup(:default, 'mysql://root:mysql@localhost/dm2_dev' )

24. Generate Model
> script/generate dm_model book amount:float date:date name:string
description:text --skip-migration
NOTE: --skip-migration is needed because the rails-datamapper integration
gem doesn't pull out the ActiveRecord dependency on migration creation
yet.

25. Finish model definition
require 'lorem'
class Book
include DataMapper::Resource
property :id, Integer, :serial => true
property :amount, Float
property :date, Date
property :name, String
property :description, Text, :lazy => true
def self.create_dummy_data(num)
num.times do |number|
t = Book.new
t.attributes = {:amount => number, :date => Time.now(),
:name => Lorem.lorem(4, false), :description => Lorem.lorem(60, false)}
t.save
end
end
end

26. Create Migration
migration 1, :create_books do
up do
create_table :books do
column :id, Integer, :serial => true, :nullable? => false, :key => true
column :amount, Float
column :date, Date
column :name, String
column :description, DataMapper::Types::Text
end
end
down do
drop_table :books
end
end

27. Create Migration Rake Task
namespace :dm do
task :migrate => :environment do
gem quot;dm-migrationsquot;
require quot;migration_runnerquot;
Dir[File.join(Rails.root, quot;dbquot;, quot;migratequot;, quot;*quot;)].each {|f| require f}
migrate_up!
end
end
src/dm2> mysqladmin create dm2_dev
src/dm2> rake dm:migrate

28. Wire up application
●
Create Controller for book
●
Create “bulk” generation capability

29. Summary Checklist
●
Add gems & generate application
●
Remove ActiveRecord & add DataMapper
●
Configure database.yml & datamapper.rb
●
Create your database
●
Generate your model, complete definition &
migrate
●
Continue defining application

30. Additional Goodness
●
Validations
●
Conditions
●
Order
●
Aggregations
●
Associations
●
Named Scope (class methods)

31. Assessment
●
Can't beat the speed
●
Outstanding flexibility
●
Durn if it won't be more complex to develop
with

32. Thank you