ActiveRecord Query Interface

ActiveRecord Query Interface 3.0

@tim_keller

Consultant at innoQ

OK. Let's Go!

In a Nutshell

The new AR Query Interface is:

Tasty!

That was it.

Just kidding!

Preamble

The new Query Interface is build on top of:

Active Relation

A GoogleSummerOfCode-Project that:

„...integrate Arel into the existing implementation of ActiveRecord...“

http://socghop.appspot.com/gsoc/student_project/show/google/gsoc2009/rails/t124025364581

„Arel is a Relational Algebra for Ruby“

http://github.com/rails/arel

And simplifies the generation of complex SQL queries

Show me some code!

Caution!

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

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

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

deprecated

Example (deprecated)

● Owner.find(:first)

● Owner.find(:first, :conditions => {:name => 'test'})

But that is OK:● Owner.find(1)

● Owner.find(1,2)

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

Example (deprecated)

● named_scope :red, :conditions => { :colour => 'red' }

● default_scope :order => 'last_name'

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

The New Shit!

New finder methods

Example (New API)

● where

● having

● select

● group

● order

● limit

● offset

● joins

● includes

● lock

● readonly

● from

The return value is a ActiveRecord::Relation

Relations are lazy loaded!

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 }

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

Example

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

● Rails 3● Owner.where(:name => 'test').first

Relations are chainable and „shareable“

Example

● Rails 3@books = Book.order(params[:order))

@published_books = @books.where(:published => true)

@unpublished_books = @books.where(:published => false)

Example

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

● Rails 3● Book.where("price <= ?",10).includes(:authors)

named_scope => scope

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')

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/

Sources

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

My two cents. Thank you!