brown bag: oo design

• dependency inversion: depend on abstractions, don’t depend on concretions.
• Liskov substitution: don’t violate superclass by using is_kind_of; they should return the same type

Test

• does it have one responsibility?
• it is DRY?
• does everything in it changes at the same rate?
• is it open for extension but not for modification?
• does it depend on things that change less often than it does?

select rows with a column that occurs more than once

SELECT lname FROM Celebrities 
  GROUP BY lname HAVING COUNT (lname) >1

after_commit

http://inductor.induktiv.at/blog/2010/09/01/after-commit-callbacks/

http://rails-bestpractices.com/posts/695-use-after_commit

http://stackoverflow.com/questions/2220788/rails-after-commit

helper and auto_increment in DB

Methods in helpers are always available in the views, and can be included in controllers.

Auto_increment for some column like id is global. So when you do transaction and you set id=4, and then it is failed; the next available id will be 5, not 4.

Ruby 1.9 changes

To read and make notes http://blog.grayproductions.net/articles/getting_code_ready_for_ruby_19

CSV is built into Ruby 1.9

In Ruby 1.9, fasterCSV has been made the implementation of the stdlib
CSV, so we remove the rubygems (which btw, is also
included by default in 1.9) and just make require 'csv' and CSV
instead of FasterCSV.

http://ruby-doc.org/stdlib/libdoc/csv/rdoc/index.html

the return of JSON parse is not string

require ‘json’

>> a={“use”=>false}
=> {“use”=>false}
>> b=a.to_json
=> “{\”use\”:false}”
>> c=JSON.parse b
=> {“use”=>false}
>> if not c[“use”]
>> puts “json parse gives true and false boolean values”
>> end
json parse gives true and false boolean values
=> nil

REST

representational state transfer

• its idea is to use HTTP to make calls between machines to get resources
• return the representation of the resource (i.e., the content type of the resource), not the resource itself.
• resources :actions is equivalent of defining four name routes to 7 controller actions: index, show, create, update, delete, edit, new
• both new and edit use GET method
• index action is usually show plural/collection resource, so is create
• resouces is actions for members, not collections, but you can add collections inside the resource loop.
• Example to know the difference between representation and resource == representation: form submission, resources: xml string， html files
• one URI corresponds to one resource; resource can be any information, one picture, one paragraph, one video
• representation is realized through respond_to

Learn REST

• http://rest.elkstein.org/?m=1
• http://blog.csdn.net/zlb824/article/details/7663606
• http://ihower.tw/rails3/restful.html

Routing

• URL mapping to action by routing in config/route.rb
• the routing rule created first has higher priority
• “rake routes” show all your routes
• “rake routes CONTROLLER=products” show all your routes in productions controller
• limit http method used to access a route match ‘products/:id’ => ‘products#show’, :via => post which is equivalent to  get ‘products/:id’ => ‘products#show’
• name a route by :as => ‘my_route_name’ so that you can link_to “MY ROUTE”, my_route_name_path
• specify a parameter in a link: link_to “MY ROUTE”, my_route_name_path(:id=>item.id)
• parameter can be objects, which is transformed to a hash by object.to_param in the model

Log

Most programming context in Rails (MVC) have a logger attribute

• view: <%= debug @user %>
• controller: logger.debug "The object is #{@object}"
• controller: return render :text => "The object is #{@object}" The render :text call will dump the text to the screen and halt execution of the current action.
• Model: logger.debug

How can we watch the log in development

• look at log/development.log
• tail -f app_root/log/development.log which will scroll the log as it gets stuff appended to it.
• -f means monitor a file, which will display the last 10 lines and append new lines to the display as new lines are added to the file
• to interrupt tail while monitoring, use ctrl+C
• less -R file -> interpret the color codes and escape sequences.

Debug rails applications

• http://guides.rubyonrails.org/debugging_rails_applications.html

FasterCSV has nothing to do with Rails framework. Is a Ruby library.