ActiveRecord 4新特性 http://www.oschina.net/translate/get-your-app-ready-for-rails-4?print
#1 Caching with Instance Variables
#2 Dynamic find_by Methods
#3 Find Through Association
#4 Move Find into Model
#5 Using with_scope
#6 Shortcut Blocks with Symbol to_proc
#16: Virtual Attributes (revised)
#17、habtm-checkboxs
#15 Fun with Find Conditions
#14 Performing Calculations on Models
#22 Eager Loading
#23 Counter Cache Column
#28 in_groups_of
#29 group_by Month
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 %>
发表评论
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rails 小技巧
2014-02-23 22:55 585#Rails Tip 1 Actions Are Method ... -
ruby 小技巧
2014-02-23 21:18 945#Track 1: The C in MVC #irb Mi ... -
rails 小代码合集 view controller model
2014-02-23 13:18 1609Rails Create an image with link ... -
rails bash
2014-02-22 21:48 6101、一个完整的rails app自动生成bash 引用#!/ ... -
实用工具--rails 命令、generator
2014-02-22 20:52 9931、rails 基本 rails new rails-boo ... -
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2014-02-22 14:02 567升级到 Rails 4,你的应用需要准备什么? 升 ... -
理解rails gems plugins
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日期 、路由辅助方法
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