Underlaying Technology of Modern O/R Mapper

RubyKaigi2011Underlaying Technology ofModern O/R Mapptermakoto kuwatahttp://www.kuwata-lab.com/

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

The Goal of Modern ORM

What is the Problem?

By the way...

Refactoring

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

Again, What is the Problem? • SQL cant break large one into pieces • SQL cant be constructed from pieces • SQL cant name or abstract pieces

Does ORM Solve it? Not abstracted

Abstract by Named Scope

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

Conclusion of this section SQL is just Assembler It cant be broken into pieces It cant be constructed from pieces It cant name or abstract pieces Modern ORM provides abstraction for SQL ex. named_scope

Query Object

Kwd arg vs. Method Chain

Query Object (1)

Query Object (2)

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

Query Operation (1) Just a method call

Query == Collection Array ActiveRecord::Relation

Action to Collection condition condition

SQL Abstraction (1)

SQL Abstraction (2)

OT: Partial Application

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

ORM and View-layer Cache

Example: Fragment Cache

Example: Controller Submits SQL everytime

Move ﬁnd() from C to V? MVC broken

Check Cache Existence? C depends on V tightly

What is the Problem? View Cache: Pull-styleMVC: Push-style Context Data Controller

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

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

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

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

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

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

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

N+1 Problem

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

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

Sol: Eager Loading

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

Sol: Strategic Eager Loading

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

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

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

Ruby-to-SQL Translation

Evaluation x=1 x+1 2

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

Operator Override

Ruby to AST to SQL == Operator x 1Override

Other Examples

Sequel Example

Pitfalls 1.8 doesnt allow to override != operator Use 1.9 Impossible to override && nor || Use & and | instead, or AND(), OR()

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

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

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

Any Questions?

http://twitter.com	10
http://www.hanrss.com	2
http://tweetedtimes.com	2
https://twitter.com	1

Underlaying Technology of Modern O/R Mapper

by kwatch on Jul 18, 2011

Accessibility

Categories

Tags

Upload Details

Usage Rights

4 Embeds 15

Statistics

Underlaying Technology of Modern O/R Mapper — Presentation Transcript