The document discusses various ways to improve Ruby and ActiveRecord syntax through custom methods and techniques like method missing. It provides examples of mapping database queries to method calls for cleaner code, handling multi-database connections, and generating classes on demand through constant missing. The overall goal is to explore how Ruby syntax and patterns can be enhanced for more readable and intuitive code.

1. Dr Nic
drnicwilliams.com
DIY Syntax

2. $ irb
>> $KCODE = quot;uquot;
>> quot;303274quot;
=> quot;üquot;

3. Isn’t this nicer?
>> U00FC
=> quot;üquot;

4. $ sudo gem install charesc
$ irb
>> $KCODE = quot;uquot;
>> require 'rubygems'
>> require 'charesc'
>> quot;charesc is made by Martin D#{U00FC}rstquot;
=> quot;charesc is made by Martin Dürstquot;
>> U00FC
=> quot;üquot;
>> quot;303274quot;
=> quot;üquot;
charesc

5. Active
Records
SELECT * FROM conferences WHERE (start_date > '2007-06-07')
# But, much nicer is...

6. Active
Records
SELECT * FROM conferences WHERE (start_date > '2007-06-07')
# But, much nicer is...
Conference.find(:all,
:conditions => [‘start_date > ?’,Date.today])

7. Active Records
SELECT conferences.quot;idquot; AS t0_r0,
conferences.quot;namequot; AS t0_r2, ...,
conference_sessions.quot;idquot; AS t1_r0,
conference_sessions.quot;conference_idquot; AS t1_r1, ...
FROM conferences
LEFT OUTER JOIN conference_sessions
ON conference_sessions.conference_id = conferences.id
WHERE (start_date < '2007-05-26')
# But, definitely easier and nicer is...

8. Active Records
SELECT conferences.quot;idquot; AS t0_r0,
conferences.quot;namequot; AS t0_r2, ...,
conference_sessions.quot;idquot; AS t1_r0,
conference_sessions.quot;conference_idquot; AS t1_r1, ...
FROM conferences
LEFT OUTER JOIN conference_sessions
ON conference_sessions.conference_id = conferences.id
WHERE (start_date < '2007-05-26')
# But, definitely easier and nicer is...
Conference.find(:all,
:conditions => ['start_date < ?', Date.today],
:include => :conference_sessions)

9. Sexy
Syntax
ActiveRecords
- no SQL
... + marshalling
to objects

10. Sexy
Syntax
Convenient
Code

11. Schemas
create_table :conferences do |t|
t.fkey :user
t.string :name, :limit => 50
t.text :description
t.date :start_date, :end_date
t.auto_dates
end
# instead of...
I can never
remember
SQL syntax

12. Schemas
create_table :conferences do |t|
t.fkey :user
t.string :name, :limit => 50
t.text :description
t.date :start_date, :end_date
t.auto_dates
end
# instead of...
Look up SQL on
I can never
remember
SQL syntax

13. Composite
Primary Keys
ProductHistory.find(:first, :conditions =>
['id = ? and start_date = ?', 56, Date.new(2000,5,5)])
# rather...
What about
Ruby syntax
improving on
other Ruby
syntax?

14. Composite
Primary Keys
ProductHistory.find(:first, :conditions =>
['id = ? and start_date = ?', 56, Date.new(2000,5,5)])
# rather...
ProductHistory.find(56, Date.new(2000,5,5))
What about
Ruby syntax
class ProductHistory < ActiveRecord::Base improving on
other Ruby
set_primary_keys :id, :start_date syntax?
end

15. What’s this do? #1
Nice syntax
can quickly tell
you want the
code will does
@user.conference_sessions_for(@conference)

16. What’s this do? #1
Nice syntax
can quickly tell
you want the
code will does
@user.conference_sessions_for(@conference)
# Returns all ConferenceSessions
# for a user at a conference

17. What’s this do? #2
@conference_attendees.map_id_and_login_and_full_name

18. What’s this do? #2
@conference_attendees.map_id_and_login_and_full_name
# map {|att| [att.id, att.login, att.full_name]}

19. What’s this do? #3
User.find(params[:id])

20. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])

21. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])
@to_user.update(@from_db::User.find(params[:id]))

22. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])
@to_user.update(@from_db::User.find(params[:id]))
# Copies a User from one database to another
# see Magic Multi-Connection
# http://magicmodels.rubyforge.org

23. Let’s see how they
work...

24. What’s this do? #1
Nice syntax
can quickly tell
you want the
code will does
@user.conference_sessions_for(@conference)

25. What’s this do? #1
Nice syntax
can quickly tell
you want the
code will does
@user.conference_sessions_for(@conference)
# Returns all ConferenceSessions
# for a user at a conference

26. What’s this do? #1
class User < ActiveRecord::Base
has_many :conference_sessions
def conference_sessions_for(conference)
conference_sessions.find(:all,
:conditions => ['conference_id = ?', conference])
end
end
No meta-magic, but it gives nice syntax

27. What’s this do? #2
@attendees.map_by_id_and_login_and_full_name
# map {|att| [att.id, att.login, att.full_name]}

28. Cute ways to use #map
@users = User.find(:all)
@users.map {|user| user.login}
# => ['drnic', 'topfunky', 'dhh']

29. Cute ways to use #map
@users = User.find(:all)
@users.map {|user| user.login}
# => ['drnic', 'topfunky', 'dhh']
@users.map &:login
# => ['drnic', 'topfunky', 'dhh']

30. Cute ways to use #map
@users = User.find(:all)
@users.map {|user| user.login}
# => ['drnic', 'topfunky', 'dhh']
@users.map &:login
# => ['drnic', 'topfunky', 'dhh']
# but it gets ugly when you chain them...
@users.map(&:login).map(&:size)
# => [5, 8, 3]

31. Cute ways to use #map
# So, instead of...
@users.map(&:login).map(&:size)
# We might like...
@users.map_login.map_size

32. Remember find_by_xxx ?
def method_missing(method_id, *arguments)
pattern = /^find_(all_by|by)_([_a-zA-Z]w*)$/
if match = pattern.match(method_id.to_s)
finder = determine_finder(match)
# from active_record/base.rb, line 1190

33. Dissecting the request
def method_missing(method, *args, &block)
pattern = /(map|select|...)_by_([w_]+??)/
if (match = method.match(pattern))
iterator, callmethod = match[1], match[2]
# changed ‘find’ to ‘map’
# or select, reject, each, collect...

34. Iterating the request
# continued...
iterator, callmethod = match[1], match[2]
self.send(iterator) {|obj| obj.send callmethod }
# @array.map_by_foo
# callmethod => ‘foo’
# #foo invoked on each element of Array

35. Iterating many callmethods
# continued...
iterator, callmethod = match[1], match[2]
callmethods = callmethod.split('_and_')
callmethods.map do |callmethod|
self.send(iterator) {|obj| obj.send callmethod }
end
# @array.map_by_foo_and_bar
# callmethods => [‘foo’, ‘bar’]
# #foo and #bar invoked on each element of Array

36. map_by_method gem
# for complete source:
$ gem install map_by_method
$ mate $RUBYGEMS_PATH/map_by_method-0.6.0/lib/map_by_method.rb

37. map_by_method gem
# for complete source:
$ gem install map_by_method
$ mate $RUBYGEMS_PATH/map_by_method-0.6.0/lib/map_by_method.rb
# add the following to your ~/.irbrc
require 'map_by_method'

38. What’s this do? #3
User.find(params[:id])

39. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])

40. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])
@to_user.update(@from_db::User.find(params[:id]))

41. What’s this do? #3
@to_user = @target_db::User.find(params[:id])
User.find(params[:id])
@to_user.update(@from_db::User.find(params[:id]))
# Copies a User from one database to another
# see Magic Multi-Connection
# http://magicmodels.rubyforge.org

42. Magic
Multi-Connections
@db::User.find(params[:id])

43. MMC - alternate ideas
@db::User.find(params[:id])
# but I would have preferred...
User.find(params[:id]).from_db(@db)

44. MMC - alternate ideas
@db::User.find(params[:id])
# but I would have preferred...
User.find(params[:id]).from_db(@db)
# but we’d need FindProxies
# like AssociationProxies

45. But what does this mean?
@db::User

46. class creator helper
class Module
def create_class(class_name, superclass = Object, &block)
klass = Class.new superclass, &block
self.const_set class_name, klass
end
end
>> module Connection; end
>> Connection.create_class 'User'
=> Connection::User

47. class creator helper
class Module
def create_class(class_name, superclass = Object, &block)
klass = Class.new superclass, &block
self.const_set class_name, klass
end
end
>> module Connection; end
>> Connection.create_class 'User'
=> Connection::User
@db::User

48. But...the class...
“when to create it?”
When you ask for it!

49. const_missing
class Module
alias :old_const_missing :const_missing
def const_missing(const_id)
return old_const_missing(const_id) rescue nil
target_class = quot;::#{const_id}quot;.constantize rescue nil
raise NameError.new(quot;bad constant #{const_id}quot;) unless target_class
create_class(const_id, target_class)
end
end

50. const_missing
class Module
alias :old_const_missing :const_missing
def const_missing(const_id)
return old_const_missing(const_id) rescue nil
target_class = quot;::#{const_id}quot;.constantize rescue nil
raise NameError.new(quot;bad constant #{const_id}quot;) unless target_class
create_class(const_id, target_class)
end
end
magic multi-connections

51. Picks up root classes
class Person; end
module Remote
establish_connection :other
end
>> Remote::Person.superclass
=> Person

52. const_missing
class Module
def const_missing(const_id)
return old_const_missing(class_id) rescue nil
table_name = DrNicMagicModels::Schema.models[const_id]
raise NameError.new(quot;bad constant #{const_id}quot;) unless table_name
create_class(class_id, ActiveRecord::Base) do
set_table_name table_name
end
end
end
“Does the class name match to a table name?”

53. const_missing
class Module
def const_missing(const_id)
return old_const_missing(class_id) rescue nil
table_name = DrNicMagicModels::Schema.models[const_id]
raise NameError.new(quot;bad constant #{const_id}quot;) unless table_name
create_class(class_id, ActiveRecord::Base) do
set_table_name table_name
end
end
dr nic’s magic models
end
“Does the class name match to a table name?”

54. const_missing
>> U00FC
=> quot;üquot;

55. const_missing
def const_missing(const)
if const.to_s =~ /^((U( [0-9ABCEF][0-9A-F]{3} # general BMP
| D[0-7][0-9A-F]{2} # excluding surrogates
| [1-9A-F][0-9A-F]{4} # planes 1-15
| 10 [0-9A-F]{4} # plane 16
)
)*
)
$/ix
unescaped = $1.split(/[Uu]/)[1..-1].collect do |hex| hex.to_i(16) end.pack('U*')

56. Sexy
Syntax
Convenient
Code

57. Enjoy En !
drnicwilliams.com
by Dr Nic