View this talk as a blog: http://alexkitchens.net/2017/05/06/rails-source-code.html Open source projects like Rails are intimidating, especially as a beginner. It’s hard to look at the code and know what it does. But Ruby on Rails is more than just code. Written into it are years of research, discussions, and motivations. Also written into it are bugs, typos, and all of the pieces that make the code human. This talk outlines steps you can take to explore the inner workings of Rails and gain context on its design. Understanding how Rails works will allow you to write better Rails applications and better Ruby code. You will leave with many resources and tips on perusing Rails.

1. @alexcameron89
PERUSING THE RAILS SOURCE CODE
A BEGINNERS GUIDE

2. ⋆ Star 30,000

3. Time
Internals
Comprehension
Me

4. Time
Internals
Comprehension
You

5. CAUTION
Side Effects
Perusing Rails

6. You might experience
an increase in
Ruby knowledge

7. You might experience
an increase in
Git knowledge

8. You might experience
enlightenment to
magic

9. Rails GitHub Repository
Rails Dependencies Setup
guides.rubyonrails.org/development_dependencies_install
github.com/rails/rails

10. actioncable
actionmailer
actionpack
activejob
guides
Gemfile
Gemfile.lock
rails.gemspec
actionview
activerecord
activesupport
activemodel
railties
MIT-LICENSE
CONTRIBUTING.md
README.md
~ ❯ cd rails/
~/rails ❯ ls

11. actioncable
actionmailer
actionpack
activejob
guides
Gemfile
Gemfile.lock
rails.gemspec
actionview
activerecord
activesupport
activemodel
railties
MIT-LICENSE
CONTRIBUTING.md
README.md
~ ❯ cd rails/
~/rails ❯ ls

12. ~ ❯ rails server

13. Request
~ ❯ rails server

14. Routes
Request
~ ❯ rails server

15. Controller
Routes
Request
~ ❯ rails server

16. Controller
Routes
Request
~ ❯ rails server
Model

17. Controller
Routes
Request
~ ❯ rails server
View
Model

18. Controller
Routes
Request
~ ❯ rails server
View
Model

19. Controller
Routes
Request
Response
~ ❯ rails server
View
Model

20. Controller
Routes
ActionPack
Request
Response
~ ❯ rails server
View
Model

21. Controller
ActiveRecord
ActiveModel
Routes
ActionPack
Request
Response
~ ❯ rails server
View
Model

22. Controller
ActiveRecord
ActiveModel
Routes
ActionPack
ActionView
Request
Response
~ ❯ rails server
View
Model

23. Controller
ActiveRecord
ActiveModel
Routes
ActionPack
ActionView
Request
Response
~ ❯ rails server
View
Model
Railties

24. Controller
ActiveRecord
ActiveModel
Routes
⋆
⋆
⋆
⋆ ActiveSupport
ActionPack
ActionView
Request
Response
~ ❯ rails server
View
Model
Railties

25. ActionMailer
Mail Delivery
ActiveJob
Jobs/Tasks
ActionCable
Integrated
WebSockets

26. +
Your Story tenderlove github
ActionMailer
Mail Delivery
ActiveJob
Jobs/Tasks
ActionCable
Integrated
WebSockets

27. +
Your Story tenderlove github
ActionMailer
Mail Delivery
ActiveJob
Jobs/Tasks
ActionCable
Integrated
WebSockets
tenderlove
Aaron Patterson
What room are you in?
South Ballroom

28. actioncable
actionmailer
actionpack
activejob
guides
Gemfile
Gemfile.lock
rails.gemspec
~/rails ❯ ls

29. lib
test
README.rdoc
activerecord.gemspec
CHANGELOG.md
bin
examples
MIT-LICENSE
RUNNING_UNIT_TESTS.rdoc
~/rails ❯ cd activerecord/
~/rails/activerecord ❯ ls

30. s.add_dependency "activesupport", version
s.add_dependency "activemodel", version
s.add_dependency "arel", "~> 8.0"
activerecord/active_record.gemspec

31. ~/rails/activerecord ❯ cd lib
~/rails/activerecord/lib ❯ ls
active_record
rails
active_record.rb

32. attributes.rb
attribute_mutation_tracker.rb
base.rb
persistence.rb
reflection.rb
relation.rb
schema.rb
. . .
~/rails/activerecord/lib ❯ cd active_record
~/rails/activerecord/lib/active_record ❯ ls

34. ~/rails/activerecord/lib ❯ cd active_record
~/rails/activerecord/lib/active_record ❯ ls
attributes.rb
attribute_mutation_tracker.rb
base.rb
persistence.rb
reflection.rb
relation.rb
schema.rb
. . .

35. ~/rails/activerecord/lib ❯ cd active_record
~/rails/activerecord/lib/active_record ❯ ls
attributes.rb
attribute_mutation_tracker.rb
base.rb
persistence.rb
reflection.rb
relation.rb
schema.rb
. . .

36. Post.find_by
# => #<Post id:1, title: "Example", ...>
Post.where
# => #<ActiveRecord::Relation [#<Post ...>]>

37. activerecord/lib/active_record/relation/finder_methods.rb
77 def find_by(arg, *args)
78 where(arg, *args).take
79 rescue ::RangeError
80 nil
81 end

38. Ǹ
Digging Through
Code With Ruby

39. Post.method(:create).source_location
~/blog ❯ rails console

40. Post.method(:create).source_location
=> [“…/lib/active_record/persistence.rb”, 29]
~/blog ❯ rails console

41. activerecord/lib/active_record/persistence.rb
29 def create(attributes = nil, &block)
. . .
33 object = new(. . .)
34 object.save
35 object
36 . . .
37 end

42. Post.new.method(:save).source_location
=> [“…/lib/active_record/suppressor.rb”, 41]

44. Persistence

45. 41: def save(*) # :nodoc:
=> 42: SuppressorRegistry.suppressed[self.class.name] ?
true : super
43: end
activerecord/lib/active_record/suppressor.rb

46. 306: def save(*) #:nodoc:
307: rollback_active_record_state! do
=> 308: with_transaction_returning_status { super }
309: end
310: end
activerecord/lib/active_record/transactions.rb

47. 34: def save(*)
=> 35: if status = super
36: changes_applied
37: end
38: status
39: end
activerecord/lib/active_record/attribute_methods/dirty.rb

48. 43: def save(options = {})
=> 44: perform_validations(options) ? super : false
45: end
activerecord/lib/active_record/validations.rb

49. 124: def save(*args)
=> 125: create_or_update(*args)
126: rescue ActiveRecord::RecordInvalid
127: false
128: end
activerecord/lib/active_record/persistence.rb

50. post = Post.new
post.method(:save).source_location
=> [“. . . /suppressor.rb”]
post.method(:save).super_method.source_location
=> [“. . . /transactions.rb”]

51. ...
require "byebug"
...
byebug
Post.create
activerecord/active_record.gemspec

52. ~/rails ❯ ls rails/guides/bug_report_templates/
action_controller_master.rb
active_job_master.rb
active_record_master.rb
active_record_migrations_master.rb
benchmark.rb
generic_master.rb

53. require "bundler/inline"
gemfile(true) do
source "https://rubygems.org"
gem "rails", github: "rails/rails"
gem "arel", github: "rails/arel"
gem "sqlite3" # or "pg" or "mysql2" . . .
end
require "active_record"
require "minitest/autorun"
require "logger"

54. require "bundler/inline"
gemfile(true) do
source "https://rubygems.org"
gem "rails", path: “path/to/your/rails“
gem "arel", github: "rails/arel"
gem "sqlite3" # or "pg" or "mysql2" . . .
end
require "active_record"
require "minitest/autorun"
require "logger"

55. ActiveRecord::Base.establish_connection(adapter: "sqlite3",
database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Schema.define do
create_table :posts do |t|
t.string :title
end
end
class Post < ActiveRecord::Base
end
. . .

56. . . .
class BugTest < Minitest::Test
def test_association_stuff
post = Post.create(title: “Hello”)
assert_equal “Hello”, post.title
end
end

57. . . .
class BugTest < Minitest::Test
def test_association_stuff
post = Post.create(title: “Hello”)
assert_equal “Hello”, post.title
end
end

58. . . .
post = Post.create(title: “Hello”)

59. require “pry”
. . .
post = Post.create(title: “Hello”)
binding.pry
[1] pry(main)>

60. require “pry”
. . .
post = Post.create(title: “Hello”)
binding.pry
[1] pry(main)> Post.all
=> [#<Post id: 1, title: "Hello">]

61. require “byebug”
. . .
byebug
Post.create(title: "Fancy Post")

62. [31, 33] in active_record_master.rb
31:
32: byebug
=> 33: Post.create
(byebug) s

63. in activerecord/lib/active_record/persistence.rb
29: def create(attributes = nil, &block)
=> 30: if attributes.is_a?(Array)
. . .
32: else
33: object = new(attributes, &block)
(byebug) n

64. in activerecord/lib/active_record/persistence.rb
29: def create(attributes = nil, &block)
30: if attributes.is_a?(Array)
. . .
32: else
=> 33: object = new(attributes, &block)
(byebug) var local

65. in activerecord/lib/active_record/persistence.rb
29: def create(attributes = nil, &block)
30: if attributes.is_a?(Array)
. . .
32: else
=> 33: object = new(attributes, &block)
(byebug) var local
attributes = {:title=>"Hello"}
block = nil

66. It can be troubling to know
simultaneously the exact value
and correct execution of a
variable.
- Werner Heisenbug

67. I know this I don’t know this
Association Reflection
Attributes
Attribute Mutation
Tracker
Relation
. . .

68. I know this I don’t know this
Association
Reflection
Attributes
Attribute Mutation
Tracker
Relation
. . .

69. Delete It

70. Delete It

71. def define_method_attribute=(name)
safe_name = name.unpack("h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb
Creates post.title=

72. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb
=> “479647c656”

73. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

74. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb
=> “__temp__479647c656”

75. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

76. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

77. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def __temp__#{safe_name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

78. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def #{name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

79. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def #{name}=(value)
. . .
end
alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
undef_method :__temp__#{safe_name}=
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

80. def define_method_attribute=(name)
safe_name = name.unpack(“h*".freeze).first
. . .
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
def #{name}=(value)
. . .
end
STR
end
activerecord/lib/active_record/attribute_methods/write.rb

81. 1) Error:
BasicsTest#test_non_valid_identifier_column_name:
SyntaxError: formal argument cannot be a global variable
def a$b=(value)
def test_non_valid_identifier_column_name
weird = Weird.create("a$b" => "value")
weird.reload
assert_equal "value", weird.send("a$b")
assert_equal "value", weird.read_attribute("a$b")
. . .
end
activerecord/lib/active_record/attribute_methods/write.rb

82. ƶ
Finding Information
With Git

83. ~/rails ❯ git blame
. . .
7c70430c Ryuta Kamizono 2016-08-23 def __temp__#{safe_name}=(value)
7c70430c Ryuta Kamizono 2016-08-23 name = . . .
7c70430c Ryuta Kamizono 2016-08-23 write_attribute(name, value)
7c70430c Ryuta Kamizono 2016-08-23 end
. . .

84. --- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -15,13 +15,13 @@ def define_method_attribute=(name)
ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
- def __temp__#{safe_name}=(value)
- name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
- write_attribute(name, value)
- end
- alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
- undef_method :__temp__#{safe_name}=
- STR
+ def __temp__#{safe_name}=(value)
+ name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
+ write_attribute(name, value)
+ end
+ alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
+ undef_method :__temp__#{safe_name}=
+ STR
end
end

85. ~/rails ❯ git blame -w
. . .
b785e921 Aaron Patterson 2013-07-03 def __temp__#{safe_name}=(value)
b785e921 Aaron Patterson 2013-07-03 name = . . .
b785e921 Aaron Patterson 2013-07-03 write_attribute(name, value)
b785e921 Aaron Patterson 2013-07-03 end
. . .

86. ~/rails ❯ git log
-S "alias_method #{(name + '=').inspect}"
commit b785e921d186753d905c1d0415b91d0987958028
Author: Aaron Patterson <lovingtenderly@tenderlove.com>
Date: Wed Jul 3 14:18:31 2013 -0700
method transplanting between modules isn't supported on 1.9
commit 55ac7db11bd2fc0cf06d7184f013018fa4be0e9a
Author: Aaron Patterson <lovingtenderly@tenderlove.com>
Date: Wed Jul 3 10:56:56 2013 -0700
keep a cache of writer methods
. . .

87. ~/rails ❯ git log
--patch
--pickaxe-all
-S "alias_method #{(name + '=').inspect}"
commit b785e921d186753d905c1d0415b91d0987958028
Author: Aaron Patterson <lovingtenderly@tenderlove.com>
Date: Wed Jul 3 14:18:31 2013 -0700
method transplanting between modules isn't supported on 1.9
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/module/method_transplanting'
+
module ActiveRecord
module AttributeMethods
@@ -62,9 +64,30 @@ def cache_attribute?(attr_name)

88. ~/rails ❯ git log
--reverse
--patch
--pickaxe-all
-S "alias_method #{(name + '=').inspect}"
commit f1765019ce9b6292f2264b4601dad5daaffe3a89
Author: Jon Leighton <j@jonathanleighton.com>
Date: Fri Oct 12 12:33:11 2012 +0100
Don't allocate new strings in compiled attribute methods
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -9,15 +9,19 @@ module Write
module ClassMethods
protected
- def define_method_attribute=(attr_name)
- if attr_name =~ ActiveModel::AttributeMethods::NAME_COMPILABLE_REGEXP

89. ❯ Initial Commit
commit baa237c974fee8023dd704a4efb418ff0e963de0
Author: Santiago Pastorino <santiago@wyeworks.com>
Date: Mon Mar 21 21:36:05 2011 -0300
Allow to read and write AR attributes with non valid identifiers

90. Vim Fugitive
GitHub

93. Learning More
with GitHub

94. DEPRECATION WARNING: `redirect_to :back` is
deprecated and will be removed from Rails 5.1.
Please use `redirect_back(fallback_location:
fallback_location)` . . .

95. ~/rails ❯ git log -S
"Please use `redirect_back(fallback_loc"

96. ~/rails ❯ git log -S
"Please use `redirect_back(fallback_loc"
commit 13fd5586cef628a71e0e2900820010742a911099
Author: Derek Prior
Date: Tue Dec 15 20:17:32 2015 -0500
Add `redirect_back` for safer referrer redirects
. . .
When there is no referrer available on the request,
`redirect_to :back` will raise `ActionController::RedirectBackError`,
usually resulting in an application error.
. . .

99. General
Rails Knowledge

100. Reproduction Script
Issue: #51367
General
Rails Knowledge

101. Reproduction Script
Issue: #51367
General
Rails Knowledge

102. Pull Request Received

103. Discussion between
Contributors & Maintainers

104. More Commits Added

105. Rebased,
Merged into master

106. ƶ

107. Takeaways from PRs & Issues

110. With reproduction steps
Attached PR

111. Resources

112. the_act_of_making_love_tenderly.rb
I am a puts debuggerer
tenderlovemaking.com
Aaron Patterson

113. you_should_tell.rb
eileencodes.com/speaking/
Breaking Down the
Barrier: Demystifying
Contributing to Rails
System Tests PR
github.com/rails/rails/pull/26703
Eileen Uchitelle

114. hi_sean_hi_derek.rb
The Bike Shed
@_bikeshed
Derek Prior
Sean Griffin
Amanda Hill

115. magical_learning_elixir.rb
Crafting Rails 4
Applications
pragprog.com
José Valim

116. fxn.rb
The Rails Boot Process
https://youtu.be/vSza2FZucV8
Xavier Noria

117. Thank You
@alexcameron89
Slides: LINK HERE