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- 1. Rails Under The Knife Jacob Harris The New York Times http://open.nytimes.com/ http://www.nimblecode.com/ harrisj@nytimes.com harrisj@schizopolis.net harrisj on Flickr / Twitter / Del.icio.us / 43whatever / NYC.rb / Last.fm / etc.
- 3. Things You Might Know • basic Ruby syntax • object-oriented programming • has_many :talks • <%= for t in @talks %> • and that it’s really @talks.each do |t| • validates_presence_of :name • def before_save(talk)
- 5. The Stuff of Magic • Three things you might kinda know: • Blocks • Reflection • Metaprogramming • Commonly called magic, but...
- 6. Code can and should be manipulated like data
- 11. Metaprogramming • Or add new code as your program runs • define_method - specify new methods for your classes as needed • method_missing - catch-all method that can support infinite methods • eval - evaluate any Ruby code (be careful) • send - dynamically invoke methods by name.
- 12. photo from Flickr user procsilas
- 14. AR Associations class Conference < ActiveRecord::Base has_many :talks end adds to the class these methods (among others): c.talks c.talks << c.talks.find c.talks.empty? c.talks.create ...
- 16. has_many def has_many(association_id, options = {}, &extension) reflection = create_has_many_reflection(association_id, options, &extension) ... collection_accessor_methods(reflection, HasManyAssociation) end
- 17. define_method def collection_reader_method(reflection, association_proxy_class) define_method(reflection.name) do |*params| association = instance_variable_get(quot;@#{reflection.name}quot;) unless association.respond_to?(:loaded?) association = association_proxy_class.new(self, reflection) instance_variable_set(quot;@#{reflection.name}quot;, association) end association end end
- 18. All Together Now def collection_reader_method(reflection, association_proxy_class) define_method(reflection.name) do |*params| association = instance_variable_get(quot;@#{reflection.name}quot;) unless association.respond_to?(:loaded?) association = association_proxy_class.new(self, reflection) instance_variable_set(quot;@#{reflection.name}quot;, association) end Metaprogramming association Blocks end Reflection end
- 19. defines methods class Conference def talks(*params) association = instance_variable_get(quot;@#{reflection.name}quot;) unless association.respond_to?(:loaded?) association = HasManyAssociation.new(self, reflection) instance_variable_set(quot;@#{reflection.name}quot;, association) end closure association end end
- 20. About That SQL class HasManyAssociation < AssociationCollection def initialize construct_sql end def construct_sql ... @finder_sql = quot;#{@reflection.klass.table_name}.# {@reflection.primary_key_name} = #{@owner.quoted_id}quot; @finder_sql << quot; AND (#{conditions})quot; if conditions end end
- 22. Where Are Those From? • class Talk < ActiveRecord::Base belongs_to :conference end • No find methods added by script/generate • Nothing being added by define_to. • It even finds new columns right when I add them to the DB (cue spooky theremin music here)
- 23. method_missing irb> 3.foo NoMethodError: undefined method `foo' for Fixnum:Class from (irb):2 class Object def method_missing(method_id, *arguments) throw NoMethodError ... end end
- 24. method_missing class ActiveRecord::Base def method_missing(method_id, *arguments) if match = /^find_(all_by|by)_([_a‐zA‐Z]w*)$/.match (method_id.to_s) finder = determine_finder(match) attribute_names = extract_attribute_names_from_match(match) super unless all_attributes_exists?(attribute_names) attributes = construct_attributes_from_arguments (attribute_names, arguments) send(finder, finder_options) else super end end
- 25. method_missing def method_missing(method_id, *arguments) if match = /^find_(all_by|by)_([_a‐zA‐Z]w*)$/.match is (method_id.to_s) if method name find_* finder = determine_finder(match) find all see if we should find one or attribute_names = extract_attribute_names_from_match(match) super unless all_attributes_exists?(attribute_names) extract columns to find by from name or extra arguments attributes = construct_attributes_from_arguments (attribute_names, arguments) call the finder with options, send(finder, finder_options) return results else super end end else super ⇌ call Object's MM ⇌ NoMethodError
- 26. Reflection
- 27. Observers class LocationObserver < ActiveRecord::Observer def before_save(location) res = MultiGeocoder.geocode(location.address) lat = res.lat lng = res.lng true end end
- 28. Calling My Observers # when your app calls Location.save def create_or_update_with_callbacks return false if callback(:before_save) == false result = create_or_update_without_callbacks callback(:after_save) result end saves to the DB
- 29. Doing The Callback :before_save def callback(method) callbacks_for(method).each do |callback| ... if callback.respond_to?(method) callback.send(method, self) end ... end Callback is an object of some type
- 30. Doing The Callback def callback(:before_save) callbacks_for(:before_save).each do |callback| ... if callback.respond_to?(:before_save) callback.send(:before_save, self) end ... end Callback is your Observer
- 31. Type Is Irrelevant Notice it's if callback.respond_to?(:before_save) NOT if callback.kind_of?(ActiveRecord::Observer)
- 32. photo from Flickr user selva
- 33. GarbageTruck acts_as_plow photo from Flickr user phrenologist
- 34. Where Classic OOP Fails class GarbageTruck < SnowPlow No Way! end class GarbageTruck include Plowing No Better! end class Plow < AbstractFrontAttachment class Truck WTF? def add_attachment(attach_object) end class GarbageTruck < Truck
- 35. The Ruby Way class GarbageTruck acts_as_plow_maybe end def acts_as_plow_maybe if snowing? define_method('plow!') do |*params| ... end end end
- 36. Blocks
- 37. λ aka
- 39. def transaction(start_db_transaction = true) transaction_open = false begin if block_given? if start_db_transaction begin_db_transaction transaction_open = true end executes your block yield end rescue Exception => database_transaction_rollback if transaction_open transaction_open = false rollback_db_transaction end raise end ensure commit_db_transaction if transaction_open end
- 40. RESTful Responding respond_to do |format| format.html # index.rhtml format.xml { render :xml => @users.to_xml } end
- 41. RESTful Responding • Rails 1.2 allows you specify different actions for different formats requested by the caller (eg, page for HTML, feed for XML, etc.) • Response behavior based on complex logic: • Caller may explicitly specify in URL • Your app may have implicit priorities specified (eg, Atom before XML) • Rails may also have to decide on one based on client HTTP request headers
- 42. RESTful Responding /talks => return the rendered index.rhtml /talks.xml => return XML format /talks.jpg => return HTTP Error 406 - “Not Acceptable”
- 43. Content Negotation Accept: text/xml,application/xml,application/ xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/ png,*/*;q=0.5 HTTP/1.1 includes the following request-header fields for enabling server-driven negotiation through description of user agent capabilities and user preferences: Accept (section 14.1), Accept-Charset (section 14.2), Accept-Encoding (section 14.3), Accept- Language (section 14.4), and User-Agent (section 14.43). However, an origin server is not limited to these dimensions and MAY vary the response based on any aspect of the request, including information outside the request- header fields or within extension header fields not defined by this specification.
- 44. Why Not A Case? case format when :html render :html when :xml render :xml => @users.to_xml end
- 45. respond_to do |format| format.html # index.rhtml format.xml { render :xml => @users.to_xml } end Outer Block - yields registry Inner Block - mime/type handler
- 46. Registering a Handler format.xml { render :xml => @users.to_xml } :xml { render :xml ... } class ActionController::MimeResponds::Responder def method_missing(symbol, &block) mime_constant = symbol.to_s.upcase if Mime::SET.include?(Mime.const_get (mime_constant)) custom(Mime.const_get(mime_constant), &block) else super stores your block to end execute for MIME match end end
- 47. Responding priority list of acceptable response MIME types def respond for priority in @mime_type_priority if priority === @order find in your list of @responses[priority].call blocks to respond_to return # mime type match found, be happy and return end end eval 'render(:nothing => true, :status => quot;406 Not Acceptablequot;)', @block_binding end error if no handlers
- 48. Thank You