The document summarizes the new ActiveRecord query interface in Rails 3. Some key points: - The new interface is built on Arel and simplifies generating complex SQL queries. - Methods like "find" with options hashes are deprecated in favor of explicit query methods like "where", "having", "select", etc. These return a lazy-loaded ActiveRecord::Relation. - Relations can be chained, shared, and loaded eagerly using "all()", "first()", etc. Named scopes are now just called "scopes". - The old query interface will be removed in Rails 3.2, so developers should update their code.

1. ActiveRecord Query Interface 3.0

2. @tim_keller

3. Consultant at innoQ

4. OK. Let's Go!

5. In a Nutshell

6. The new AR Query Interface is:

7. Tasty!

8. That was it.

9. Just kidding!

10. Preamble

11. The new Query Interface is build on
top of:

12. Active Relation

13. A GoogleSummerOfCode-Project
that:

14. „...integrate Arel into the existing
implementation of ActiveRecord...“
http://socghop.appspot.com/gsoc/student_project/show/google/gsoc2009/rails/t124025364581

15. „Arel is a Relational Algebra for
Ruby“
http://github.com/rails/arel

16. And simplifies the generation of
complex SQL queries

17. Show me some code!

18. Caution!

19. The „old“ ActiveRecord Query
Interface will be deprecated in Rails
3.1 and fully removed in Rails 3.2!

20. The „options hash“ for ActiveRecord
class methods is now deprecated

21. MyClass.find(:first) and
MyClass.find(:last) are also
deprecated

22. Example (deprecated)
● Owner.find(:first)
● Owner.find(:first, :conditions =>
{:name => 'test'})
But that is OK:
● Owner.find(1)
● Owner.find(1,2)

23. The „options hash“ for the Scope
stuff is also deprecated

24. Example (deprecated)
● named_scope :red, :conditions =>
{ :colour => 'red' }
● default_scope :order => 'last_name'

25. „named_scope“ is deprecated in
Rails 3.0. Just use „scope“

26. The New Shit!

27. New finder methods

28. Example (New API)
● where
● having
● select
● group
● order
● limit
● offset
● joins
● includes
● lock
● readonly
● from

29. The return value is a
ActiveRecord::Relation

30. Relations are lazy loaded!

31. Example
● Rails 2
● Owner.find(:first, :conditions =>
{:name => 'test'})
● Rails 3
● Owner.where(:name => 'test')
● with DB-Query
– Owner.where(:name => 'test').each{ |o|
puts o.name }

32. For Eager Loading use all(),
first(), last()

33. Example
● Rails 2
● Owner.find(:first, :conditions =>
{:name => 'test'})
● Rails 3
● Owner.where(:name => 'test').first

34. Relations are chainable and
„shareable“

35. Example
● Rails 3
@books = Book.order(params[:order))
@published_books = @books.where(:published =>
true)
@unpublished_books = @books.where(:published =>
false)

36. Example
● Rails 2
● Book.find(:all, :conditions => ["price
<= ?", 10], :include => :authors)
● Rails 3
● Book.where("price
<= ?",10).includes(:authors)

37. named_scope => scope

38. Example
● Rails 2
● named_scope :red, :conditions => {
:colour => 'red' }
● Rails 3.0
● scope :red, :conditions => { :colour
=> 'red' }
● Rails 3.2
● scope :red, where(:colour => 'red')

39. Sources
● m.onkey.org/2010/1/22/active-record-query-
interface
● magicscalingsprinkles.wordpress.com/2010/01/
28/why-i-wrote-arel/
● edgeapi.rubyonrails.org/
● slideshare.net/GreggPollack/rails-3-beautiful-
code-3219240
● flickr.com/photos/fofurasfelinas/2502823019/siz
es/o/

40. Sources
● flickr.com/photos/timcaynes/148110505/
● flickr.com/photos/gurana/3831997459/sizes/m/

41. My two cents. Thank you!