merb – The Pocket Rocket Framework

Rowan Hick @ Toronto Rails Night, June 2008

(Adapted S9 Version from Original PDF Slide Deck)

Discussion tonight

  • Intended for people who don’t know what Merb is
  • Good grasp of Rails concepts
  • Not patient enough to google/irc/blog search etc to get started on Merb
  • Touch on a lot of features
  • All links/references up on work.rowanhick.com tomorrow

About Rowan Hick

  • Product Development Mgr for a startup in Toronto
  • Full time with Rails for 2.5 years
  • Previously PHP/MySQL for 4 years
  • 6 years Prior QA/BA/PM for Enterprise CAD/CAM software dev company

Objects of Desire

Super Bike

Sport Cars

  • What are these doing in a presentation about Ruby web frameworks?

Bikes vs Cars

The Porsche, you just open the door, turn the key, and drive. It has a/c, a stereo, plush upholstery, everything. Accidents can and do happen but few and far between, but pretty user friendly.

The sports bike, it’s raw, unadulterated. You can’t hop on it wrapped in cotton wool, way easier to get burned. However it’s faster, easier to replace, modify and tune things at a lower cost.

Parallels to the world of MVC?

Rails is…

  • Very user friendly & well documented
  • suitable for 80% most web projects
  • a turn-key framework.

...and

Merb is…

  • aiming for that other 20%
  • fast as all hell
  • going to require a little more skill to get up and running with
  • “the framework for hackers”

Same same but different

  • It’s actually quite similar! (workflow, layout)
  • However … don’t start emailing merb groups asking for feature XYZ to be implemented “like it is in Rails”
  • Don’t expect your app to port without code changes to Merb (although you’d be suprised how little needs to change)

Who Built it

Key Philosophy

  • All you need and none you don’t
  • No code is faster than no code
  • Anything that slows Merb down is a bug (my personal favourite)

Merb-core -more gems

  • What the? Isn’t it just Merb?
  • merb-core is the basic slimmed down bare minimum code
  • merb-more contains niceties to help you along your way (action-args, assets, builder, cache, freezer, gen, haml, jquery, mailer, parts, slices)

Switzerland

  • Merb is the Switzerland of Ruby frameworks
  • Doesn’t care that you might favour Datamapper over ActiveRecord
  • Lets you choose ORM, Test Framework, JS Framework, Rack Adaptor

Getting started

To start off with get both core and more

gem install merb-core merb-more

Choose your ORM

  1. gem install merb-activerecord
  2. gem install sequel
  3. gem sources -a http://gems.datamapper.org && sudo gem install addressable english rspec data_objects do_mysql do_postgres do_sqlite3 dm-core dm-more

merb-gen

  • Your new friend
  • generates code/files for your app
rowan$ merb-gen app speeddemon
 RubiGen::Scripts::Generate
   create log
   create app
     ...etc
  • merb-gen app yourapp --flat (or) --very-flat (puts your application on a serious diet)

Differences

. Rails Merb
Routes config/routes.rb config/router.rb
Initialization config/environment.rb config/init.rb
Environment specific config/environments/* config/environments/*
Plugins vendor/plugins gems
Migrations db/migrate schema/migrations
Testing test test (or) spec
Public public public
Models app/models app/models
Controllers app/controllers app/controllers
Helpers app/helpers app/helpers
Lib lib/ (config in init.rb)

vendor/plugins gems

  • Everything is a gem
  • Freeze your gems with your app
  • gem install -i somegem ~/yourapp/gems/—no-ri—no-rdoc
  • convert rails plugins, start with merb-gen plugin plugin_name
  • Lots underway github.com/search?q=merb

edit config/init.rb

Choose your ORM

use_orm: activerecord
use_test: rspec

Include dependencies (eg mailer)

dependencies "merb_helpers", "merb-parts" 
Merb::BootLoader.after_app_loads do
  # Add dependencies here that must load after the
application loads:
  dependencies "merb-mailer" 
  # dependency "magic_admin" # this gem uses the
app's model classes
end

I want my database.yml

Patience. Because you’ve told merb you want active record, just fire merb for the first time:

rowan-laptop:speeddemon rowan$ merb
 ~ Loaded DEVELOPMENT Environment...
 ~ loading gem 'merb_activerecord' ...
 ~ loading gem 'activerecord' ...
 ~ No database.yml file found in /Users/rowan/testing/speeddemon/config.
 ~ A sample file was created called database.sample.yml for you to copy and edit.

Copy, edit and save.

merb-gen generators

Let’s you know what you can create automagically:

rowan-laptop:b2b_merb rowan$ merb-gen generators

.....

Installed Generators

  Rubygems: authenticated, controller, database_sessions_migration,
migration, model, part_controller, resource, resource_controller

see more rubigen.rubyforge.org

merb-gen model mymodel

Synonymous with script/generate mymodel

Extra points:

  • dependent on ORM – creates migration or not
  • dependent on test framework – creates spec or unit test

Setup your first REST resource

  • merb-gen again
$ merb-gen resource Product title:string
  • Sets up controller, views, model, test code
  • Get coding!

Controller code

Looks reasonably similar:

class Products < Application
  before :check_access_level
  provides :xml

  def index
    @products = Product.find(:all, :order => :sort_order )
    display @products
  end

  def show
    @product = Product.find_by_product_id(params[:id])
    raise NotFound unless @product
    display @product
  end
  ...

Key Differences

Rails Merb
products_controller products
redirect_to( hash ) redirect( string )
respond_to provides / only_provides / display
before/after_filter before/after
except exclude
render(hash) *optional render or render('hello world') *mandatory to get a view
logger merb.logger
url_for url

display

  • Display handles mime type response
provides :xml
def index
  @product = Product.find(params[:id])
  display @product
end
  • Goto http://127.0.0.1:4000/product/2.xml
  • Display then looks for index.xml.erb, if not found then calls @product.to_xml

Syntactic sugar

  • Making controller methods look more like methods
def my_action(id)
  product = Product.find(id)
end
  • Automagically assigns id from params[:id]
  • In merb-more (merb-action-args)

Part Controllers

  • Reusable ‘components’ for use in your views
  • Not accessible from outside world, but can see params hash
  • Their own generator
  • Again in merb-more (merb-parts)

Implementing Parts

In config/init.rb

dependency 'merb-parts'

Use merb-gen to set it up for you

$ merb-gen part_controller widget
...
create app/helpers/widget_part_helper.rb
create app/parts/widget_part.rb
create app/parts/views/widget_part/index.html.erb

Edit action(s) then call it from a view

<%= WidgetPart => :index %>

Exceptions

  • Handled in app/controllers/exceptions.rb
def show
  @product = Product.find_by_product_id(params[:id])
  raise NotFound unless @product
  display @product
end
  • exceptions.not_found method
  • render out in that view what you want to show for that error

Router is Powerful

Example from Yehudas slides at RailsConf

Merb::Router.prepare do |r|
  r.match(%r{/login/(.*)}, :user_agent => /MSIE/).
  to(:controller => "acount",
     :action => "login",
     :id => "[1]" 
end

Pressing the GO button

  • Simple
merb -p 3000 -e development
  • Fires up a mongrel instance through merb
  • Hit it just like regular old rails app

Hooking up to webserver

  • Merb implements a Rack adaptor
  • Allows you to use different types of application server depending on your needs. Example:
merb -p 3000 -e production -a thin
  • Mongrel, Thin, Ebb, Eventd Mongrel, Passenger
  • Connect Apache/Nginx -> Merb (not) Apache -> Mongrel -> Merb

Resources

The million dollar question

Should I use it ?