Most Rails users are familiar with ActiveRecord. But what does that mean? What is ActiveRecord's approach to object relational mapping? And what are the alternatives?

1. Rails and Alternative
ORMs
Dan Weinand
Jonathan Dahl

2. Why?

4. DB vs. OO
declarative vs. imperative

5. DB vs. OO
char/text vs. string

6. DB vs. OO
schema vs. _______

7. DB vs. OO
joins vs. pointers

8. DB vs. OO
public vs. encapsulated

9. DB vs. OO
constraints vs. validation

10. DB vs. OO
_____ vs. inheritance

11. DB vs. OO
DBA vs. programmer

12. DB vs. OO
structure vs. behavior

14. http://www.engrish.com//wp-content/uploads/2008/08/hand-grenade.jpg

15. 1. ActiveRecord

16. An object that wraps a row in a database table or view,
encapsulates the database access, and adds domain logic on
that data.
Martin Fowler, PoEAA, 160.

17. One object per row.

18. Data access and domain
logic are done together.

19. 6 Criticisms
of ActiveRecord

20. 1. Too much magic.
http://cgi.ebay.com/MEDIEVAL-MAGE-KING-BLACK-TUNIC-COSTUME-SCA-LARP-_W0QQitemZ250373576829QQcmdZViewItemQQimsxZ20090215?IMSfp=TL090215143008r8810#ebayphotohosting

21. class User < ActiveRecord::Base
end

22. 2. Not performant.
http://www.flickr.com/photos/danprates/1418154518/

23. 3. Not thread safe.
No connection pooling.
http://www.flickr.com/photos/streetmuseo/57990915/

26. 4. Hides SQL from you.
http://www.momentaryfascinations.com/entertainment/the.lost.monty.python.cartoon/still.5.jpg

27. 5. Hard to fight against.
http://www.mmonotebook.com/wp-content/uploads/2008/04/larp.jpg

28. 6. Encourages stupid databases.

29. 9 ways to bypass
application-level
constraints

30. 1. Fixtures

31. 2. Klass.delete(1)

32. 3. record.save(false)

33. 4.

34. 5. Share DB with a
second app

35. 6. User.create(:company_id => 1)

36. class User < ActiveRecord::Base
7. has_many :posts
end

37. 8. ActiveRecord::Base.connection.execute()

38. 9. Errors in your app
logic

39. 2. Sequel

40. An object that wraps a row in a database table or view,
encapsulates the database access, and adds domain logic on
that data.
Martin Fowler, PoEAA, 160.

41. Ruby DSL for SQL
posts = DB[:posts]
posts.filter(:category => /ruby/i, :author => [:jon, :dan])
posts.reverse_order(:created_at, :updated_at)
posts.select(:title, :author)
posts.limit(10)

42. Ruby-like DSL for SQL
posts.filter(:category => :ruby).order(:created_at).select(:title, :author)

43. ORM
class Post < Sequel::Model
many_to_many :tags
many_to_one :author
validates_presence_of :title
end
post = Post[123]
post.title # quot;rails ormsquot;
post.title = quot;Rails ORMsquot;
post.save

44. 3 interesting things
sequel postgres://localhost:5432/myapp_development

45. 3 interesting things
require 'memcache'
CACHE = MemCache.new 'localhost:11211', :namespace => 'blog'
class Author < Sequel::Model
set_cache CACHE, :ttl => 3600
end
Author[333] # database hit
Author[333] # cache hit

46. 3 interesting things
DB = Sequel.sqlite('app_test.db',
:servers=>{:read_only=>{:host=>'slave_server'}})

47. 3. Datamapper

48. A layer of Mappers (473) that moves data between objects and
a database while keeping them independent of each other and
the mapper itself.
Martin Fowler, PoEAA, 165.

49. Multiple Databases
• SQL-based
• In-memory
• Document-based
• Search engines

50. Explicit property mapping
class Message
include DataMapper::Resource
property :name, String
property :body, Text
property :created_at, DateTime
validates_presence_of :name
end

51. Get only the data you need

52. Minimize the number of
queries

53. Save only the data that
has changed

54. Identity Map
repository do
@parent.children.each do |child|
puts @parent.object_id = child.parent.object_id
end
end

55. Ruby Query Syntax
Zoo.first(:name.eql => 'Galveston')
Person.all(:age.gt => 30)
Person.all(:age.gte => 30)
Person.all(:name.not => 'bob')
Person.all(:name.like => 'S%', :id => [1,2,3,4,5])
Person.all(:name.not => ['bob','rick','steve'])
Person.all(:order => [:age.desc])

56. Chainable finders
class Zoo
def self.open
all(:open => true)
end
def self.big
all(:animal_count.gte => 1000)
end
end
big_open_zoos = Zoo.big.open

57. Associations
class Article
include DataMapper::Resource
property :id, Serial
property :title, String
property :content, Text
belongs_to :author
end
class Author
include DataMapper::Resource
property :id, Serial
property :name, String
has n, :articles
end
Article.all('author.name' => 'Michael')

58. Implicit and explicit
migrations

59. Only basic functionality
in core

60. Gems for everything else

61. Is it ready for
primetime?

62. Roadmap to 1.0

63. Rails integration still
lacking

64. Not many production
deployments

65. Documentation sucks

66. Some plugins still not
ported

67. Thanks!
Dan Weinand
Jon Dahl