SOLID Ruby, SOLID Rails

Michael Mahlberg, Consulting Guild AG
Jens-Christian Fischer, InVisible GmbH

SOLID Ruby -
SOLID Rails
Establishing a sustainable
codebase

Founder of

roughly a dozen companies
over the last two decades

Working as

A consultant on software
processes, architecture &
design for > 2 decades

Who?

Jens-Christian Fischer

Tinkerer, Practician,
Author
and generally
interested in way
too many things

PPP
(by Robert C. Martin)

Agile Software
Development,
Principles, Patterns,
and Practices

Principles!

You know - more
like guidelines

SOLID

SRP OCP L
S O LSP I
ISP DIP
D

SRP
Single
Responsibility
Principle

SRP
Single
Responsibility
Principle

A class should have
one, and only one,
reason to change.

User Class
require 'digest/sha1'

class User < ActiveRecord::Base
include Authentication
include Authentication::ByPassword
include Authentication::ByCookieToken

#TODO Check login redirect if this filter is skipped
#skip_after_filter :store_location

# Virtual attribute for the unencrypted password
attr_accessor :password

belongs_to :country

has_one :user_profile, :dependent => :destroy
has_one :note

has_many :queries
has_many :tags, :foreign_key => "created_by"
has_many :taggings, :as => :tagger
has_many :organizations, :through => :affiliations
has_many :affiliations
has_many :locations, :through => :affiliations
has_many :projects, :through => :memberships
has_many :memberships
has_many :public_assets, :through => :privileges
has_many :descriptions, :through => :privileges
has_many :assessments, :through => :privileges
has_many :description_profiles, :through => :privileges
has_many :privileges
has_many :diaries
has_many :roles, :through => :commitments
has_many :commitments
has_many :activities
has_many :messages
has_many :fellowships

end

def editable_by?(user=nil)
self.created_by == user
end

def readable_by?(user=nil)
self.created_by == user
end

def boards
User Class
Board.all :conditions => { :user_group_id => self.user_groups.collect{ |g| g.id }}
end

def discussions
Discussion.all :conditions => { :board_id => self.boards.collect{ |b| b.id }}
end

def organization_roles
role_ids = Affiliation.all(:conditions => {:user_id => self.id}).collect{|a| a.role_id}.uniq
roles = Role.ﬁnd(role_ids)
end

def user_group_roles
role_ids = Fellowship.all(:conditions => {:user_id => self.id}).collect{|a| a.role_id}.uniq
end

def project_roles
role_ids = Membership.all(:conditions => {:user_id => self.id}).collect{|a| a.role_id}.uniq
end

def all_roles
roles = (self.organization_roles + self.user_group_roles + self.project_roles).uniq
end

def tags_of(user)
taggings = Tagging.all :conditions => {:taggable_type => "User", :taggable_id => self.id, :tagger_type => "User", :tagge
tags = taggings.collect {|t| t.tag.name}.uniq.sort
end

So what‘s wrong with
this?

From: user.rb
...
belongs_to :country
...
has_one :user_profile, :dependent => :destroy
has_many :queries
has_many :tags, :foreign_key => "created_by"
...
validates_presence_of :login, :email, :country_id
validates_presence_of :password, :if => :password_required?
...

From: user.rb
acts_as_state_machine :initial => :pending

state :pending, :enter => :make_activation_code
state :active, :enter => :do_activate
...
event :register do
transitions :from => :passive, :to => :pending, :guard =>
Proc.new {|u| !(u.crypted_password.blank? &&
u.password.blank?) }
end
...
def message_threads
self.message_threads + self.message_threads
end

From: user.rb
def forum_nickname
self.user_profile.nickname.blank? ? "#{self.first_name}
#{self.last_name}" : self.user_profile.nickname
end

def name
"#{self.first_name} #{self.last_name}" rescue 'n/a'
end

def email_with_name
"#{self.first_name} #{self.last_name} <#{self.email}>"
end

From: user.rb
def is_admin?
self.roles.collect{|role| role.title}.include?('admin')
end

def countries
[self.country]
end

From: user.rb
def boards
Board.all :conditions => { :user_group_id =>
self.user_groups.collect{ |g| g.id }}
end

def discussions
Discussion.all :conditions => { :board_id =>
self.boards.collect{ |b| b.id }}
end

def organization_roles
role_ids = Affiliation.all(:conditions => {:user_id =>
self.id}).collect{|a| a.role_id}.uniq
roles = Role.find(role_ids)
end

From: user.rb
def make_password_reset_code
self.password_reset_code =
Digest::SHA1.hexdigest( Time.now.to_s.split(//).sort_by
{rand}.join )
end

def self.published_users
User.all(:conditions => ['state = ?',
'published'], :order => 'login ASC', :include =>
[:user_profile])
end

Authentication
Roles
Mailers
State
...

New User Model

include Project::UserStates
include Project::UserMailer
include Project::UserForum
include Project::UserMessages
...
end

UserMessages
module Project
module UserMessages
# to be included in User Model

has_many :messages
def message_threads
MessageThread.all(:conditions =>
["sender_id = ? or receiver_id = ?",
self.id, self.id])
end
end
end

def transfer(data, url)
h = Net::HTTP.new(self.uri.host, self.uri.port)
RAILS_DEFAULT_LOGGER.debug "connecting to CL: #{self.uri}"
RAILS_DEFAULT_LOGGER.debug "connecting to CL: #{url}"

resp = h.post(url, data, {'Content-Type' => 'application/xml'})
response_code = resp.code.to_i
location = if response_code == 201
resp['Location']
else
RAILS_DEFAULT_LOGGER.debug "error from CL: #{response_code}"
RAILS_DEFAULT_LOGGER.debug "error from CL: #{resp.body}"
@error = resp.body
nil
end
[response_code, location]
end

def transfer(data, document)

if document.cl_document_url != nil
self.uri = URI.parse(document.cl_document_url )
response = h.post(self.uri, data, {'Content-Type' =>
'application/xml'})
else
response = h.post("/tasks", data, {'Content-Type' =>
'application/xml'})
end
response_code = response.code.to_i
if response_code == 201
location = response['Location']
document.cl_document_url = location
document.save!
else
nil
end
[response_code, location]
end

SRP Transfer
def transfer data
open_connection
post data
return location
end

def open_connection
@http = Net::HTTP.new(self.uri.host, self.uri.port)
end

def post data
@response = http.post(self.url, data, {'Content-Type' =>
'application/xml'})
end

def location
get_location if created? # returns nil if not created?
end

def response_code
@response.code.to_i
end

def created?
response_code == 201
end

def get_location
@response['Location']
end

def error
@response.body
end

Add a 16-band
equalizer & a
BlueRay®
player to this...

OCP
Open
Closed
Principle

OCP
Open
Closed
Principle

You should be able
to extend a classes
behavior, without
modifying it.

From the Google
AI Challenge
(Tronbot)

def makemove(map)
From the Google
x, y = map.my_position
# calculate a move ... AI Challenge
if(valid_moves.size == 0)
map.make_move( :NORTH )
(Tronbot)
else
# choose move ...
puts move # debug (like in the old days)
map.make_move( move )
end
end

class Map
...
def make_move(direction)
$stdout << ({:NORTH=>1, :SOUTH=>3, :EAST=>2, :WEST=>4}[direction])
$stdout << "n"
$stdout.flush
end
end

From the Google AI Challenge (Tronbot)

From the Google AI Challenge (Tronbot)
def puts(*args)
$stderr.puts *args
end

def p(*args)
args.map!{|arg| arg.inspect}
puts args
end

def print(*args)
$stderr.print *args
end

class Outputter

def initialize(io = $stderr)
@io = io
end

def puts(*args)
@io.puts *args
end

...
end

out = Outputter.new
out.puts "Testing"

LSP
Liskov
Substitution
Principle

LSP
Liskov
Substitution
Principle

Derived classes
must be substitutable
for their base
classes.

No Problem
in Ruby

Or so it seems...

No Interface...

no problem?

Rectangle

setX
setY

Square

setX
setY

Rectangle
>> class Rectangle
>> attr_accessor :width, :height
>> end
=> nil
>>
?> shape = Rectangle.new
=> #<Rectangle:0x10114fad0>
>> shape.width
=> nil
>> shape.width=3
>> shape.width
=> 3
>> shape.height=5
>> shape.height
=> 5
>> shape.width
=> 3

Square

?> shape = Square.new
=> #<Square:0x101107e88>
?> puts shape.width
nil
?> shape.width=3
=> 3
?> shape.width
=> 3
?> shape.height
=> 3

Square
>> class Square
?> def width
>> @dimension
?> shape = Square.new
>> end
=> #<Square:0x101107e88>
?> def height
?> puts shape.width
>> @dimension
nil
>> end
?> shape.width=3
?> def width= n
=> 3
>> @dimension = n
?> shape.width
>> end
=> 3
?> def height= n
?> shape.height
>> @dimension = n
=> 3
>> end
>> end

A Problem...
>> s = [Rectangle.new, Square.new]
=> [#<Rectangle:0x1005642e8>, #<Square:0x100564298>]
>> a_rectangle = s[rand(2)]

Text

A Problem...
=> #<Square:0x100564298>
>> a_rectangle.height=1
=> 1
>> a_rectangle.width=3
=> 3
Text
>> a_rectangle.height

A Problem...
=> #<Square:0x100564298>
>> a_rectangle.height=1
=> 1
>> a_rectangle.width=3
=> 3
Text
>> a_rectangle.height
=> 3

CCD Common Conceptual
Denominator

http://blog.objectmentor.com/articles/2007/02/17/
liskov-substitution-principle-and-the-ruby-core-libraries

irb 1:0> 5.respond_to? :dup


=> true


=> true
irb 2:0> 5.dup


=> true
irb 2:0> 5.dup
TypeError: can't dup Fixnum
from (irb):1:in `dup'
from (irb):1
irb 3:0>


ISP
Interface
Segregation
Principle

ISP
Interface
Segregation
Principle

Make fine grained
interfaces that are
client specific.

Users Controller
class UsersController < ApplicationController

ssl_required :new, :create, :edit, :update, :destroy, :activate,
:change_passwort, :forgot_password, :reset_password, :make_profile,
:my_contacts
ssl_allowed :eula, :index, :show

access_control
[:suspend, :unsuspend, :destroy, :purge, :delete, :admin, :ban, :remove_ban] =>
'admin'

before_filter :find_user

skip_after_filter :store_location

def show
unless @user == current_user
redirect_to access_denied_path(@locale)
else
respond_to do |format|
format.html
format.js { render :partial => "users/#{@context.title}/#{@partial}" }
end
end
end
...

more UsersController
def activate
logout_keeping_session!
user = User.find_by_activation_code(params[:activation_code]) unless
params[:activation_code].blank?

case
when (!params[:activation_code].blank?) && user && !user.active?
user.activate!
flash[:notice] = t(:message_sign_up_complete)
unless params[:context].blank?
redirect_to login_path(:context => params[:context])
else
redirect_to "/login"
end
when params[:activation_code].blank?
flash[:error] = t(:message_activation_code_missing)
redirect_back_or_default("/")
else
flash[:error] = t(:message_user_with_that_activation_code_missing)
end
end

User Class Revisited
...
end

class Registration < ActiveRecord::Base
set_table_name "users"

acts_as_state_machine :initial => :pending

state :pending, :enter => :make_activation_code
state :active, :enter => :do_activate
...

event :activate do
transitions :from => :pending, :to => :active
end
...
end

class RegistrationController < ApplicationController
...
def activate
logout_keeping_session!
code_is_blank = params[:activation_code].blank?
registration =
Registration.find_by_activation_code(params[:activation_code]) unless
code_is_blank

case
when (!code_is_blank) && registration && !registratio.active?
registration.activate!
flash[:notice] = t(:message_sign_up_complete)
unless params[:context].blank?
redirect_to login_path(:context => params[:context])
else
redirect_to "/login"
end
when code_is_blank
flash[:error] = t(:message_activation_code_missing)
else
flash[:error] = t(:message_user_with_that_activation_code_missing)
end
end
...

DIP
Dependency
Inversion
Principle

DIP
Dependency
Inversion
Principle

Depend on
abstractions, not on
concretions.

From our OCP example to DIP

out = Outputter.new
out.puts "Testing"

The code we wish we had
class TronBot
def initialize
@@out = TRON_ENVIRONMENT[:debugger]
end

def some_method
...
@@out.puts "Testing"
...
end

end

TSTTCPW

TRON_ENVIRONMENT = {
:debugger => Outputter.new ($stderr),
:game_engine => Outputter.new ($stdout),
:user_io => Outputter.new ($stderr)
}

Later...

TRON_ENVIRONMENT = {
:debugger => Outputter.new ($stderr),
:game_engine => Outputter.new (TCP_OUTPUTTER),
:user_io => Outputter.new ($stderr)
}

DIP Violation in Controller
format.js do
render :update do |page|
if @parent_object.class == EspGoal
@esp_goal_descriptor = @current_object
page.replace_html "descriptor_#{@current_object.id}",
:partial => "edit_esp_goal_descriptor",
:locals => {:esp_goal_descriptor => @esp_goal_descriptor,
:parent_object => @parent_object}
else
@goal_descriptor = @current_object
:partial => "edit_goal_descriptor",
:locals => {:goal_descriptor => @goal_descriptor,
end
end
end

DIP Violation in Controller
format.js do
if @parent_object.class == EspGoal
@esp_goal_descriptor = @current_object
:partial => "edit_esp_goal_descriptor",
:locals => {:esp_goal_descriptor => @esp_goal_descriptor,
else if @parent_object.class == Goal
@goal_descriptor = @current_object
:partial => "edit_goal_descriptor",
:locals => {:goal_descriptor => @goal_descriptor,
else if @parent_object.class == LearningGoal
...
...
end
end
end

1st Refactoring
def show
...
format.js do
@parent_object.page_replacement(@current_object)
end
end
end

class EspGoal
def page_replacement child
{ :partial => "edit_esp_goal_descriptor",
:locals => {:esp_goal_descriptor => child,
:parent_object => self}
}
end
end

class Goal
def page_replacement child
{ :partial => "edit_goal_descriptor",
:locals => {:goal_descriptor => child,
:parent_object => self}
}
end
end

class EspGoalReplacmenent
2nd Refactoring
def self.my_class_sym

end
EspGoal.to_sym (Behaviour)
def partial_definition child
{ :partial => "edit_esp_goal_descriptor",
:locals => {:esp_goal_descriptor => child,
:parent_object => child.esp_goal}
}
end
end

class GoalReplacmenent
def self.my_class_sym
Goal.to_sym
end
def partial_definition child
{ :partial => "edit_goal_descriptor",
:locals => {:goal_descriptor => child,
:parent_object => child.goal}
}
end
end

2nd Refactoring
(wiring)
class PartialContainer
def add class_symbol, partial_replacement
@@partinal_replacements.add( class_symbol => partial_replacement)
end

def self.partial_replacement an_object
unless @@partial_replacments
self.add( EspGoalReplacement.my_class_sym, EspGoalReplacment.new)
self.add( GoalReplacement.my_class_sym, GoalReplacment.new)
end
@@partial_replacement[an_object.class]
end
end

2nd Refactoring
- the Controller -

2nd Refactoring
- the Controller -
def show
...
format.js do
PartialContainer.partial_replacement(@parent_object).
partial_definition(@current_object)
end
end
end

S O L I D Questions?

SRP OCP LSP ISP DIP

Coding Dojo
Wednesday 11:10
Salon 3
The Way of the carpenter is to
become proﬁcient in the use of
his tools, ﬁrst to lay his plans with a
true measure and then perform his
work according to plan.

– Go Rin No Sho

Credits (1/2)
PPP-Article (online)
http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Photos
http://www.flickr.com/photos/dieterkarner/370967891/
http://www.flickr.com/photos/popcorncx/2221630487/sizes/l/
http://www.flickr.com/photos/bdesham/2432400623/
http://www.flickr.com/photos/popcorncx/2221630487/
http://www.flickr.com/photos/glennbatuyong/4081599002/in/photostream/
http://www.flickr.com/photos/glennbatuyong/4081599168/in/photostream/
http://www.flickr.com/photos/renfield/3865907619/

91

Credits (2/2)
Photos
http://www.flickr.com/photos/renfield/3865907619/
http://www.flickr.com/photos/maxpower/5160699/
http://programmer.97things.oreilly.com/wiki/index.php/Uncle_Bob
http://www.flickr.com/photos/georgivar/3288942086/
http://www.everystockphoto.com/photo.php?imageId=237523
http://www.flickr.com/photos/pasukaru76/3992935923/

92

Lizense

http://creativecommons.org/licenses/by-sa/
3.0/de/

93

Jens-Christian Fischer Michael Mahlberg

InVisible GmbH Consulting Guild AG

@jcﬁscher @MMahlberg

jens-christian@invisible.ch mm@michaelmahlberg.de

http://blog.invisible.ch http://agile-aspects.blogspot.com

94

Get the Presentation
http://github.com/MichaelMahlberg/RailsWayCon2010

95

SOLID Ruby, SOLID Rails

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