ActiveRecord

ActiveRecord 4新特性 http://www.oschina.net/translate/get-your-app-ready-for-rails-4?print

ActiveRecord 范围需要一个 Callable 对象。

在 Rails 4 中，所有 ActiveRecord 范围必须使用一个 callable 对象来定义：
#Rails 3.2
scope :recent, where(created_at: Time.now - 2.weeks)
#Rails 4
scope :recent, -> { where("created_at > ?", Time.now - 2.weeks).order("created_at desc") }
scope :active, -> { where(status: 'active') }

Activerecord-deprecated-finders 是 Rails 4.0 中默认提供废弃功能的依赖包，但它也将在 4.1 版本中被删除。因此你需要密切关注所有的警告信息，并开始修复这些警告。

Rails 指南 提供一个很有用的解释，关于在大多数情况下如何修改动态查找器：

    所有动态的方法除了 findby… 和 findby…! 外都已废弃，你可以使用如下的替代方法：

find_all_by_...改为 where(...).
find_last_by_...改为 where(...).last.
scoped_by_...改为 where(...).
find_or_initialize_by_...改为 where(...).first_or_initialize.
find_or_create_by_...改为 find_or_create_by(...) 或者 where(...).first_or_create.
find_or_create_by_...!改为 find_or_create_by!(...) 或者 where(...).first_or_create!.

#1 Caching with Instance Variables

@current_user ||= User.find(session[:user_id])

#2 Dynamic find_by Methods

@tasks = Task.find(:all, :conditions => ['complete = ?', false])
=>
@tasks = Task.find_all_by_complete(false)

@task = Task.find(:first, :conditions => ['complete =?', false], :order => 'created_at DESC')
=>
@task = Task.find_by_complete(false, :order => 'created_at DESC')

#3 Find Through Association

from
@tasks = Task.find(:all, :conditions => ['project_id = ? AND complete = ?', @project.id, false])

to (推荐使用，用association 进行关联)
@project = Project.find(params[:id])
@tasks = Task.find(:all, :conditions => ['project_id = ? AND complete = ?', @project.id, false])

 
#4 Move Find into Model

Move a find into the model to clean up the controllers and remove duplication. 
将 find 转移到model中，清洁controllers
from 

class TaskController < ApplicationController
  def index
    @tasks = Task.find_all_by_complete(:false, :order => "created_at DESC")
  end
end

to
class Task < ActiveRecord::Base
  belongs_to :project
  def self.find_incomplete
    find_all_by_complete(:false, :order => "created_at DESC")
  end
end

#5 Using with_scope

class Task < ActiveRecord::Base
  belongs_to :project

  def self.find_incomplete(options = {})
    with_scope :find => options do
      find_all_by_complete(false, :order => 'created_at DESC')
    end
  end
end
@tasks = @project.tasks.find_incomplete :limit => 20

#6 Shortcut Blocks with Symbol to_proc

projects.collect { |p| p.name } => ["Write another ASCIIcast", "Go out walking"]
projects.collect {&:name}       => ["Write another ASCIIcast", "Go out walking"]
projects.collect(&:name).collect(&:upcase)  => ["WRITE ANOTHER ASCIICAST", "GO OUT WALKING"]

projects.each {|project| project.save!}
==
projects.each(&:save!)

#16: Virtual Attributes (revised)

简介：对原生的attributes(collums)，进行逻辑封装

schema.rb
create_table "products", :force => true do |t|
  t.string   "name"
  t.integer  "price_in_cents"
  t.datetime "released_at"
  ... ...
end

1、转换 {price_in_cents => price_in_dollars}


<%= f.label :price_in_dollars %>
<%= f.text_field :price_in_dollars %>

attr_accessible :name, :price_in_dollars
def price_in_dollars
  price_in_cents.to_d/100 if price_in_cents
end
def price_in_dollars=(dollars)
  self.price_in_cents = dollars.to_d*100 if dollars.present?
end

2、对 released_at 进行逻辑封装  {release_at => relese_at_text}

  attr_writer :released_at_text
  validate :check_released_at_text
  before_save :save_released_at_text
  def released_at_text
    @released_at_text || released_at.try(:strftime, "%Y-%m-%d %H:%M:%S")
  end
  
  def save_released_at_text
    self.released_at = Time.zone.parse(@released_at_text) if @released_at_text.present?
  end
  
  def check_released_at_text
    if @released_at_text.present? && Time.zone.parse(@released_at_text).nil?
      errors.add :released_at_text, "cannot be parsed"
    end
  rescue ArgumentError
    errors.add :released_at_text, "is out of range"
  end


3、支持创建新的 category
  <%= f.label :category_id %><br />
  <%= f.collection_select :category_id, Category.order(:name), :id, :name %>
  or create one:<%= f.text_field :new_category %>

  attr_accessible  :new_category
  attr_accessor :new_category  
  before_save :create_category  #在保存 product 前，先前所依赖的 category创建出来
  
  def create_category
    self.category = Category.create!(name: new_category) if new_category.present?
  end

#17、habtm-checkboxs

典型的多对多的关系 ，且使用关联表Categorization
class Product < ActiveRecord::Base
  has_many :categorizations
  has_many :categories, through: :categorizations
end

class Categorization < ActiveRecord::Base
  belongs_to :category
  belongs_to :product
end

class Category < ActiveRecord::Base
  has_many :categorizations
  has_many :products, through: :categorizations
end

rails consle分析
p=produc.first 	=> select "products".* from "products" limit 1
p.category_ids	=> select categories.id from categories inner join categorizations on categories.id=categorization.category_id where categorizations.product_id=1
p.category_ids=[1,2] =>
1、select * from categories where id IN (1,2)
2、select * from categories inner join categorizations on categoris.category_id=categorization.category_id where categorizations.product_id=1
3、insert into categorizations ... values category_id=1,product_id=1
4、insert into categorizations ... values category_id=2,product_id=1
p.categories	=>[#<Category id=1 .....>,#<Category id=2 ....>]
	

_form.html.erb

  <%= hidden_field_tag "product[category_ids][]", nil %>
  <% Category.all.each do |category| %>
    <%= check_box_tag "product[category_ids][]", category.id, @product.category_ids.include?(category.id), id: dom_id(category) %>
    <%= label_tag dom_id(category), category.name %>
  <% end %>
</div>

#15 Fun with Find Conditions

# When searching for null values the correct syntax would be priority IS NULL, not priority = NULL
Task.find(:all, :conditions => ["completed = ? AND priority = ?", false, 2]) 
SELECT * FROM "tasks" WHERE (completed = 'f' AND priority = 2)


Task.find(:all, :conditions => ["complete=? and priority IS ?", false, nil])
SELECT * FROM "tasks" WHERE (completed = 'f' AND priority is NULL) 

Task.find(:all, :conditions => ["complete=? and priority IN (?)", false, [1,3]])
Task.find(:all, :conditions => ["complete=? and priority IN (?)", false, 1..3])

Task.find(:all, :conditions => { :complete => false, :priority => 1 })
Task.find(:all, :conditions => { :complete => false, :priority => nil })

Task.find(:all, :conditions => { :completed => false, priority => [1,3] } 
SELECT * FROM "tasks" WHERE (completed = 'f' AND priority IN (1,3)

Task.find(:all, :conditions => {:completed => false, priority => 2..4})
SELECT * FROM "tasks" WHERE ("tasks"."priority" BETWEEN 2 AND 4 AND "tasks"."completed" = 'f') 

Task.find_by_priority(1..5)
SELECT * FROM "tasks" WHERE ("tasks"."priority" BETWEEN 1 AND 5) LIMIT 1

#14 Performing Calculations on Models

Task.first.priority      => 3
  SELECT * FROM "tasks" LIMIT 1
  
Task.sum(:priority)     => 12 
  SELECT sum("tasks".priority) AS sum_priority FROM "tasks"
  
Task.sum(:priority, :conditions => {:completed => false }) => 2 
  SELECT sum("tasks".priority) AS sum_priority FROM "tasks" WHERE (completed="f")
  
Task.minimum(:priority)   => 2 
  SELECT min("tasks".priority) AS min_priority FROM "tasks" 
  
Task.maximum(:priority)   => 5 
  SELECT max("tasks".priority) AS max_priority FROM "tasks"
  
Task.average(:priority).to_f  => 3.0 
  SELECT avg("tasks".priority) AS avg_priority FROM "tasks"
  
  #Using the methods through associations.
project = Project.first => #<Project id: 1, title: "A Project">   
project.tasks.sum(:priority, :conditions => {:completed => true})  => 10 
  
  SELECT sum("tasks".priority) AS sum_priority FROM "tasks" 
  WHERE ("tasks"."completed" = 't') AND ("tasks".project_id = 1)

#22 Eager Loading

<% @tasks.each do |task| %>
  <li><%= link_to task.name, task %> in <%= task.project.name %></li>
<% end %>


terminal

Project Load (0.2ms)   SELECT * FROM "projects" WHERE ("projects"."id" = 60) 
 CACHE (0.0ms)   SELECT * FROM "projects" WHERE ("projects"."id" = 60) 
 CACHE (0.0ms)   SELECT * FROM "projects" WHERE ("projects"."id" = 60) 
 CACHE (0.0ms)   SELECT * FROM "projects" WHERE ("projects"."id" = 60) 
 CACHE (0.0ms)   SELECT * FROM "projects" WHERE ("projects"."id" = 60)
 
解决方案
1、eager loading reduce the calls to the database even further. 
We enable it by making a change in the TasksController.


class TasksController < ApplicationController
  def index
    @tasks = Task.find(:all, :include => :project)
  end
end


2、Including More Than One Association

class Task < ActiveRecord::Base
  belongs_to :project
  has_many :comments
end

class TasksController < ApplicationController
  def index
    @tasks = Task.find(:all, :include => [:project, :comments])
  end
end

3、more complex associations. 

class Comment < ActiveRecord::Base
  belongs_to :task
  belongs_to :user
end

@tasks = Task.find(:all, :include => [:project, {:comments => :user }])

#23 Counter Cache Column

class Task < ActiveRecord::Base
  belongs_to :project, :counter_cache => true
  has_many :comments
end

migrations/006_add_tasks_count.rb
def self.up
  add_column :projects, :tasks_count, :integer, :default => 0
  Project.reset_column_information
  Project.find(:all).each do |p|
    Project.update_counters p.id, :tasks_count => p.tasks.length
  end
end
def self.down
  remove_column :projects, :tasks_count
end

console
p = Project.first
=> #<Project id: 61, name: "Project 1", created_at: "2009-01-26 20:34:36", updated_at: "2009-01-26 22:05:22", tasks_count: 20>
>> p.tasks.create(:name => "New task")
=> #<Task id: 1201, name: "New task", project_id: 61, created_at: "2009-01-26 22:24:13", updated_at: "2009-01-26 22:24:13">

The project’s counter cache has been updated.

#28 in_groups_of

ruby teminal

  a = (1..12).to_a   => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  a.in_groups_of(4)  => [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
  a.in_groups_of(3)  => [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]
  a.in_groups_of(5)  => [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, nil, nil, nil]]
  a.in_groups_of(5, false)  => [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12]]
  a.in_groups_of(5, 0)  => [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, 0, 0, 0]]

rails

<table>
    <% @tasks.in_groups_of(4) do |tasks| %>
    <tr>
      <% tasks.each do |task| %>
      <td><%= task.name %></td>
      <% end %>
    </tr>
    <% end %>
</table>

#29 group_by Month

a = (1..20).to_a            => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
a.group_by { |num| num/5 }  => {0=>[1, 2, 3, 4], 1=>[5, 6, 7, 8, 9], 2=>[10, 11, 12, 13, 14], 3=>[15, 16, 17, 18, 19], 4=>[20]}

class TasksController < ApplicationController
  def index
    @tasks = Task.all
    @task_months = @tasks.group_by { |t| t.due_at.beginning_of_month }
  end
end

<% @task_months.keys.sort.each do |month| %>
<h2><%= month.strftime("%B %Y") %></h2>
  <% for task in @task_months[month] %>
    <p><b><%= task.name %></b> due at <%= task.due_at.to_date.to_s(:long) %></p>
  <% end %>
<% end %>