Rails Best Practices の警告をちゃんと考える ref: http://qiita.com/diskshima/items/a19273f14705bbdb3e14

file0.erb

<% unless @member.name.present? %>
  名無しの権兵衛
<% end %>

file1.erb

<% unless @member.name? %>
  名無しの権兵衛
<% end %>

file10.erb

<%= render 'member_names', members: @members %>

file11.rb

class MembersController < ApplicationController
    :
  def update_phone_number
    @member = Member.find(params[:id])

    phone_number = phone_number_params[:phone_number]

    @member.is_temporary = true
    @member.phone_number = remove_non_digit(phone_number)

    @member.save
  end
    :
end

file12.rb

class Member < ActiveRecord::Base
    :
  # ロジックはモデルの中に書く
  def update_phone_number(phone_number)
    self.is_temporary = true
    self.phone_number = remove_non_digit(phone_number)
    save
  end
    :
end

class MembersController < ApplicationController
    :
  def update_phone_number
    @member = Member.find(params[:id])
    phone_number = phone_number_params[:phone_number]
    @member.update_phone_number(phone_number)
  end
    :
end

file13.rb

get 'posts/get_post'

file14.rb

post 'posts/update_post'

get 'posts/get_post'

file15.rb

resources :posts

file16.rb

class CreateUsers < ActiveRecord::Migration
  def change
    create_table "computer" do |t|
     t.string :name
     t.integer :os_id

     t.timestamps
    end

    add_index :users, :os_id  # <= これですね
  end
end

file2.rb

member.last_name.kana

file3.rb

class member
    :
  def last_name_kana
    last_name.kana
  end
    :
end

member.last_name_kana

file4.rb

def show
  @members = Member.all    <%# インスタンス変数に値を設定 %>
end

file5.erb

  <%= render partial: 'member_names' %>   <%# ここで暗黙に @members を渡しているのと同じ %>

file6.erb

<%# @members に依存しているけど、このファイルを開くまでは分からない %>
<%= @members.map { |m| m.name } %>

file7.erb

  <%= render patial: 'member_names', locals: { members: @members } %>   <%# 明示的にローカル変数として渡している %>

file8.erb

<%# ローカル変数を使う %>
<%= members.map { |m| m.name } %>

file9.erb

<%= render partial: 'member_names', locals: { members: @members } %>