Presentation slides at RubyKaigi2011

1. RubyKaigi2011
Underlaying Technology of
Modern O/R Mappter
makoto kuwata
http://www.kuwata-lab.com/

2. Table of Contents
The Goal of Modern ORM
Query Object
View-layer Cacing
Ruby-to-SQL Transformation
How to Prevent SQL Injection

3. The Goal of Modern ORM

4. What is the Problem?

5. By the way...

6. Refactoring

7. Key Points
Programming language can
break large part into small pieces
construct large part from small pieces
add name to pieces in order to abstract
them

8. Again, What is the Problem?
• SQL can't break large one into pieces
• SQL can't be constructed from pieces
• SQL can't name or abstract pieces

9. Does ORM Solve it?
Not abstracted

10. Abstract by Named Scope

11. History of Evolution
OOP,
Modern ORM
Functional
C, Pascal DBI, ORM
Assembler SQL

12. Conclusion of this section
SQL is just Assembler
It can't be broken into pieces
It can't be constructed from pieces
It can't name or abstract pieces
Modern ORM provides abstraction for
SQL
ex. named_scope

13. Query Object

14. Kwd arg vs. Method Chain

15. Query Object (1)

16. Query Object (2)

17. Method Call vs. Query Op
Just a method call
Operation to Query object

18. Query Operation (1)
Just a method call

19. Query Operation (2)
Just a method call

20. Query Operation (3)
Just a method call

21. Query Operation (4)
Just a method call

22. Query == Collection
Array
ActiveRecord::Relation

23. Action to Collection
condition
condition

24. SQL Abstraction (1)

25. SQL Abstraction (2)

26. OT: Partial Application

27. Conslution of this section
Query object
is the key concept for modern ORM
behaves like a collection
abstracts SQL

28. ORM and View-layer Cache

29. Example: Fragment Cache

30. Example: Controller
Submits SQL everytime

31. Move find() from C to V?
MVC broken

32. Check Cache Existence?
C depends on V tightly

33. What is the Problem?
View
Cache: Pull-style
MVC: Push-style
Context Data
Controller

34. Sol: Proc or Lambda (C)
find(:all) is not called yet

35. Sol: Proc or Lambda (V)
Call find(:all) only when
cache is expired

36. Sol: Proc or Lambda
Pros.
Easy to understand & implement
Cons.
Caching on V affects to C
(C must be changed according to V)

37. Sol: Lazy Loading (C)
SQL is not executed yet

38. Sol: Lazy Loading (V)
Nothing to be changed!

39. Sol: Lazy Loading
Pros.
Caching on V doesn't affect to C
Cons.
Availables only on modern ORM
(not available on Rails2)

40. Conclusion of this section
MVC and fragment cache are not good
friends
MVC: push-style
Fragment cache: pull-style
Laziness solves them
Proc or lambda
Lazy loading

41. N+1 Problem

42. What is N+1 Problem? (1)
Team : Member = 1 : N

43. What is N+1 Problem? (2)
}1
}N

44. Sol: Eager Loading

45. Sol: Eager Loading
Pros.
Easy to understand
Cons.
Not adaptive to changes
Easy to forget
Hard to notice
Unused eager loading is very waste

46. Sol: Strategic Eager Loading

47. Sol: Strategic Eager Loading
• Each item knows its collection
• Collection resolves relationships

48. Sol: Strategic Eager Loading
Pros.
Adaptive to changes
(No need to specify relationship for eager
loading)
Cons.
Not supported in Rails (2 & 3)

49. Conclusion of this section
Eager loading
Easy to forget, hard to notice
Strategic Eager Loading
No need to specify relation names
Adaptive to changes

50. Ruby-to-SQL Translation

51. Evaluation
x=1
x+1 2

52. AST by Evaluation
x = Column.new(:x)
x+1 +
x 1

53. Operator Override

54. Ruby to AST to SQL
==
Operator x 1
Override

55. Other Examples

56. Sequel Example

57. Pitfalls
1.8 doesn't allow to override '!=' operator
Use 1.9
Impossible to override '&&' nor '||'
Use '&' and '|' instead, or 'AND()', 'OR()'

58. OT: Operast
Library to convert Ruby expression into
other language (such as SQL).
https://github.com/kwatch/operast

59. OT: Oktest
New-style testing library for Python
Apply Operator Override to Testing
http://packages.python.org/Oktest/

60. Conclusion of this section
How to
Ruby to AST (by Operator Override)
AST to SQL

61. Any Questions?