Slides from a talk I gave about using the Ruby on Rails console (and irb) to develop Web applications. Describes the features of the console, and how you might want to use it.

1. Using the Rails console
Reuven M. Lerner
reuven@lerner.co.il
September 13th, 2010

2. Some basics
• Ruby is interpreted
• Last definition wins!
• Runtime message sending (“method call”)
decision-making
• Open classes

3. The wrong way
Write in
IDE

4. The wrong way
Write in Done?
IDE

5. The wrong way
Write in Done? Try in
IDE browser

6. The wrong way
It worked!
Write in Done? Try in
IDE browser

7. The wrong way
It worked!
Write in Done? Try in
Failed?
IDE browser

8. The wrong way
It worked!
Write in Done? Try in
Failed? Use
IDE browser debugger

9. The wrong way
It worked!
Write in Done? Try in
Failed? Use
IDE browser debugger
Retry!

10. The Ruby way

11. The Ruby way
Write in
IDE
Try in
console

12. The Ruby way
Write in
Test IDE
fails?
Write a
test
Try in
console

13. The Ruby way
Write in
Test IDE
fails?
Write a Done? Try in
test browser
Try in
console

14. The Ruby way
It worked!
Write in
Test IDE
fails?
Write a Done? Try in
test browser
Try in
console

15. The Ruby way
Read logs,
backtrace
It worked!
Write in
Test IDE
fails?
Write a Done? Try in Failed? Try in
test browser console
Try in
console
Debugger

16. Whoa, that’s a lot!
• The idea is that the code is an extension of
your thoughts
• By “swimming through” and “playing with”
the code, you understand it better, and can
work with it faster

19. irb
• Interactive Ruby! (Comes with Ruby)
• Fire it up, and type Ruby code
• Define variables, classes, modules, methods
• All definitions disappear when you exit
• (Except for persistent storage, of course)

20. Why use irb?
• Test code
• Debug code
• Try things out
• Better understand Ruby
• Better understand an object or class

21. Rails requires more
• development/test/production environments
• ActiveRecord
• Other libraries, such as ActiveSupport
• HTTP requests and responses
• Model and controller objects
• Included gems

22. script/console
• Wrapper around irb
• Loads objects that are useful
• Makes other objects easily available
• Test your code, data, and assumptions

23. Invoking script/console
• script/console
• ruby scriptconsole (Windows version)
• ruby script/console
• script/console production

24. When?
• Always.
• It’s very rare for me to work on a Rails
project without a console open
• The console is where I test my objects,
experiment with code that’s longer than
one line, and try to debug my code

25. Simple IRB stuff
• Enter any Ruby code you want!
• Result of evaluation is displayed on the
screen

26. Examples
>> 5 + 5
=> 10
>> "foo".reverse
=> "oof"
>> "foo".reverse.first
=> "o"

27. Printing vs. value
>> puts "hello"
hello
=> nil
>> ['foo', 'bar', 'baz'].each do |word|
?> puts word
>> end
foo
bar
baz
=> ["foo", "bar", "baz"]

28. Printing vs. value
>> puts "hello" This is what it prints
hello
=> nil
>> ['foo', 'bar', 'baz'].each do |word|
?> puts word
>> end
foo
bar
baz
=> ["foo", "bar", "baz"]

29. Printing vs. value
>> puts "hello" This is what it prints
hello
=> nil This is its value
>> ['foo', 'bar', 'baz'].each do |word|
?> puts word
>> end
foo
bar
baz
=> ["foo", "bar", "baz"]

30. Printing vs. value
>> puts "hello" This is what it prints
hello
=> nil This is its value
>> ['foo', 'bar', 'baz'].each do |word|
?> puts word
>> end
foo This is what it prints
bar
baz
=> ["foo", "bar", "baz"]

31. Printing vs. value
>> puts "hello" This is what it prints
hello
=> nil This is its value
>> ['foo', 'bar', 'baz'].each do |word|
?> puts word
>> end
foo This is what it prints
bar
baz
=> ["foo", "bar", "baz"]
This is its value

32. Multi-line irb
irb(main):001:0> class Blah
irb(main):002:1> def sayit
irb(main):003:2> puts "hi"
irb(main):004:2> end
irb(main):005:1> end
=> nil

33. Multi-line irb
Open a class
irb(main):001:0> class Blah
irb(main):002:1> def sayit
irb(main):003:2> puts "hi"
irb(main):004:2> end
irb(main):005:1> end
=> nil

34. Multi-line irb
Open a class
irb(main):001:0> class Blah
irb(main):002:1> def sayit (Re)define a method
irb(main):003:2> puts "hi"
irb(main):004:2> end
irb(main):005:1> end
=> nil

35. Multi-line irb
Open a class
irb(main):001:0> class Blah
irb(main):002:1> def sayit (Re)define a method
irb(main):003:2> puts "hi"
irb(main):004:2> end
irb(main):005:1> end
=> nil Notice the prompt, showing line
numbers and block levels

36. Multi-line irb
Open a class
irb(main):001:0> class Blah
irb(main):002:1> def sayit (Re)define a method
irb(main):003:2> puts "hi"
irb(main):004:2> end
irb(main):005:1> end
=> nil Notice the prompt, showing line
Returns nil numbers and block levels

37. Requiring files, gems
>> require 'afile'
>> gem 'afile'

38. Variable assignment
• It works perfectly!
• Local, instance variables both work — but
instance variables don’t buy you anything
• Except namespace conflict avoidance
• Assignments disappear when irb exits

39. Variable assignment
h = {:a => 1, :b => 2}
a = [1, 2, 3, [h, h]]
@p = Person.first
@p = Person.all

40. Variable assignment
h = {:a => 1, :b => 2}
a = [1, 2, 3, [h, h]]
@p = Person.first
@p = Person.all Dynamic typing!

41. Viewing variables
>> a
=> [1, 2, 3, [{:b=>2, :a=>1}, {:b=>2, :a=>1}]]
>> h[:c] = 3
=> 3
>> a
=> [1, 2, 3, [{:b=>2, :a=>1, :c=>3},
{:b=>2, :a=>1, :c=>3}]]

42. Inspecting objects
• Just type the object’s name
>> @bob
=> #<User:0x2645874
@new_record=true,
@attributes={"name"=>"Bob",
"job"=>"Test Dummy"}>
• notice instance variables and attributes

43. Inspect with YAML
puts @bob.to_yaml
• Or:
y @bob

44. Classes, modules, and
methods
• You can define any or all of these
• Definitions work, and stick around for the
duration of the irb session
• Invisible to your running application
• When you exit, the definitions disappear

45. Defining classes
>> class Train
>> attr :passengers
>> def initialize
>> @passengers = [ ]
>> end
>> end
=> nil
>> t = Train.new
=> #<Train:0x102f391e0 @passengers=[]>
>> t.passengers << 'Reuven'
=> ["Reuven"]
>> t.passengers << 'Atara'
=> ["Reuven", "Atara"]

46. Defining classes
>> class Train
>> attr :passengers
>> def initialize
>> @passengers = [ ]
>> end
>> end Class definitions evaluate to nil
=> nil
>> t = Train.new
=> #<Train:0x102f391e0 @passengers=[]>
>> t.passengers << 'Reuven'
=> ["Reuven"]
>> t.passengers << 'Atara'
=> ["Reuven", "Atara"]

47. Define a new
ActiveRecord class
>> class Blah < ActiveRecord::Base
>> end
=> nil
>> Blah.first
ActiveRecord::StatementInvalid: RuntimeError: ERROR
C42P01 Mrelation "blahs" does not exist P15
Fparse_relation.c L857 RparserOpenTable:
SELECT * FROM "blahs" LIMIT 1

48. Define a new
ActiveRecord class
>> class Blah < ActiveRecord::Base
>> end
=> nil
Runtime message binding
>> Blah.first
ActiveRecord::StatementInvalid: RuntimeError: ERROR
C42P01 Mrelation "blahs" does not exist P15
Fparse_relation.c L857 RparserOpenTable:
SELECT * FROM "blahs" LIMIT 1

49. Avoiding huge output
• Person.all will return many records — and
thus print many records
• Assignment returns the assigned value
• Put a “;nil” after your command, and it’ll
evaluate to null, without any output!
•@people = Person.all; nil

50. Made a mistake?
• Use control-c to return to the top level
>> ['foo','bar','bat'].each do |word|
?> [1,2,3].each do |num|
?> ^C
>>

51. Exiting from irb
• Type “exit”
• That’ll return you to the shell

52. ActiveRecord
• ActiveRecord classes are available
• Console talks to the database for the
current environment
• Type the name of a class to see its fields
• Use class methods
• Create instances, use instance methods

53. ActiveRecord fields
>> Person
=> Personid: integer, email_address:
string, first_name: string, last_name:
string, password: string,
administrator: boolean, created_at:
datetime, updated_at: datetime,
avatar_file_name: text,
avatar_content_type: string,
avatar_file_size: integer,
avatar_updated_at: datetime

54. Class methods
Person.count
Person.first
Person.all
Person.find(:all, :conditions
=> ["name like ? ", "%euve%"])

55. Named scopes
• If you have a named scope:
named_scope :created_since, lambda
{ |since| { :conditions =>
['created_at >= ? ', since] }}
• Then it’s available as a class method, and we
can run it from inside of the console
>> Node.created_since('2010-9-1')

56. Huh? Named scopes?
• Don’t worry — we’ll get to those in an
upcoming session
• They’re really great, though!

57. Testing validity
>> @p = Person.new
=> #<Person id: nil, email_address: nil, first_name:
nil, last_name: nil, password: nil, administrator:
nil, created_at: nil, updated_at: nil,
avatar_file_name: nil, avatar_content_type: nil,
avatar_file_size: nil, avatar_updated_at: nil>
>> @p.valid?
=> false

58. Method differences
>> @p.save
=> false
>> @p.save!
ActiveRecord::RecordInvalid: Validation failed: First
name can't be blank, Last name can't be blank, Email
address can't be blank, Email address - Invalid email
address, Password can't be blank

59. Experiment
>>
@p.update_attributes(:first_na
me => 'Reuven')
>> @george =
Person.find_by_name('George')
>> @bob =
Person.find_by_name('Bob')

60. Reloading
reload!
• Do this every time you change a model
• You will probably have to re-create instances
of ActiveRecord objects
• Otherwise, odd things can happen

61. Fat models =
easier testing
• ActiveRecord methods are immediately
available in the console
• This means that you can test your code
more easily when it’s in ActiveRecord
• Fat models win again!
• Remember: Keep your controllers skinny

63. Sandbox
• script/console production --sandbox
• Reverts all changes that you made to the
database
• Allows you to work on your production
database without having to worry that
you’ll destroy things

64. Helpers
• Helpers: Methods for use within views
• Available under the “helper” object
• There are lots of helpers, and they have lots
of options. Test them before they’re in your
views!

65. Helper examples
>> helper.number_to_currency(123.45)
=> "$123.5"
>> helper.number_to_currency(123.45, :precision => 1)
=> "$123.5"
>> helper.pluralize(2, 'person')
=> "2 people"
>> helper.pluralize(2, 'knife')
=> "2 knives"

66. Who defined a helper?
>> helper.method(:add_tag_link)
=> #<Method:
ActionView::Base(ApplicationHelper)#add_tag_link>
>> helper.method(:truncate)
=> #<Method:
ActionView::Base(ActionView::Helpers::TextHelper)#tru
ncate>
>> helper.method(:number_to_currency)
=> #<Method:
ActionView::Base(ActionView::Helpers::NumberHelper)#n
umber_to_currency>

67. The “app” object
• Represents the Web application
• Useful for:
• Controllers
• URLs
• Routes

68. What URL?
>> app.url_for(:controller
=> :account)
=> "http://www.example.com/account"
>> app.url_for(:controller
=> :account, :action => :login)
=> "http://www.example.com/account/
login"

69. Submit requests
>> app.get '/account/login'
=> 200
>> app.post '/account/login_action', {:email_address
=> 'reuven@lerner.co.il', :password => 'password'}
=> 200
>> app.session
=> {"flash"=>{:notice=>"Sorry, but no user exists
with that e-mail address and password. Please try
again."}}
>> app.cookies
=>
{"_nlcommons_session"=>"4bd4fb842ef5f5dfdc4c09fc05e0c
a2c"}

70. Handle redirects
>> app.get '/'
=> 302
>> app.get_via_redirect '/'
=> 200
>> app.path
=> "/account/login"

71. Look at the response
>> app.get '/account/login'
=> 200
>> app.response.response_code
=> 200
>> app.response.body[0..100]
=> "<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Transitional//EN"n "http://www.w3.org/TR/
xhtml1"
>> app.response.has_flash?
=> false

72. ri
• Get documentation from within irb/console:
>> ri 'String#new'
>> ri 'String#length'
• Works really nicely, but it can take a long
time to execute

73. .irbrc
• Code is executed every time you run IRB
or console
• If a line causes trouble, it silently fails and
stops reading the file
• Yes, this is really dumb
• Great for loading files, configuration
settings

74. Naming .irbrc in Win32
• Name the file whatever you want
• Set the environment variable IRBRC to
point to that file
• Done!

75. IRB configuration
• IRB (and the console) is an essential tool
• There are many configuration parameters
and gems you can use to enhance it
• They’re great!

76. Configuration in Ruby!
• IRB.conf is a hash
• Set elements of this hash in .irbrc to change
the configuration

77. AUTO_INDENT
IRB.conf[:AUTO_INDENT]=true
• When you start a block, the prompt indents
you a little bit
• It’s not super-smart, but better than nothing

78. Autocomplete
• Should be automatic (or :USE_READLINE)
• Type TAB to complete things:
>> abc = 5
=> 5
>> abd = 6
=> 6
>> ab[tab]
abc abd abort

79. Emacs-style editing
• Control-l
• Control-p, Control-n
• Control-a, Control-e
• Control-b, Control-f
• Control-d
• Control-r for reverse search!

80. Emacs-style editing
• Control-l
• Control-p, Control-n
• Control-a, Control-e
• Control-b, Control-f
• Control-d
• Control-r for reverse search! My favorite

81. Save history
require 'irb/ext/save-history'
IRB.conf[:USE_READLINE] = true
IRB.conf[:SAVE_HISTORY] = 1000
IRB.conf[:HISTORY_PATH] =
File::expand_path("~/.irb.hist
ory")

82. ap — awesome_print
gem install awesome_print
>> h = {:a => [1,2,3], :b =>
'hello'}

83. Nicely printed
>> ap h
{
:b => "hello",
:a => [
[0] 1, (Color not shown here)
[1] 2,
[2] 3
]
}

84. >> ap Person.last
#<Person:0x7fd3acafcad0> {
:id => 50877,
:email_address => "foo@bar.wanadoo.co.uk",
:encrypted_password => "stanman42",
:first_name => "Foo",
:last_name => "Barman",
:address => "3 Foo Way",
:city => "Congleton",
:state_id => 1,
:zip_code => "CW12 1LU",
:phone_number => "01260 999999",
:payment_method_id => 2,
:notes => nil,
:receive_mailings_p => false,
:admin_p => false,
:deleted_p => false,
:heard_of_us_via => nil,
:agree_to_policy_p => true,
:monthly_payment_limit => 300,
:monthly_book_limit => 50,
:visitor_source_id => nil,
:link_admin_p => false
}

85. wirble — color output!
• gem install wirble
• In your .irbrc:
require 'wirble'
Wirble.init
Wirble.colorize

86. What returns X?
require 'what_methods'
>> 'abc'.what? 'a'
"abc".first == "a"
=> ["first"]

87. Summary
• Use the console!
• The more you use the console, the more
comfortable you’ll feel with Ruby
• It will save you lots of time and effort

88. Inspiration
• Amy Hoy’s “slash7” blog (http://slash7.com/
2006/12/21/secrets-of-the-rails-console-
ninjas/)
• “Err the blog” posting “IRB mix tape” (http://
errtheblog.com/posts/24-irb-mix-tape)
• StackOverflow posting on “favorite IRB
tricks” (http://stackoverflow.com/questions/
123494/whats-your-favourite-irb-trick)

89. Contacting me
• Call me in Israel: 054-496-8405
• Call me in the US: 847-230-9795
• E-mail me: reuven@lerner.co.il
• Interrupt me: reuvenlerner (Skype/AIM)