skills.otl

SECTION1 - Rails
        1.Enumerable inject用法:User.limit(2).inject({}) {|h, u| h[u.id]=u.email;h} #return {1=>"test1@test.com", 2=>"test2@test.com"};
        2.查看所有precompile的assets文件 y Rails.application.config.assets.paths
        3..gitignore没有作用的解决方法
          git rm . -r --cached
          git add .
          git commit -m "fixed untracked files"
        4.install fish shell on ubuntu
          #install fish shell
          sudo apt-add-repository ppa:fish-shell/release-2
          sudo apt-get update
          sudo apt-get install fish
          # set fish shell as default shell
          chsh -s /usr/bin/fish
        5.ActiveRecord::StatementInvalid: PG::Error: ERROR:  for SELECT DISTINCT, ORDER BY expressions must appear in select list的解决方法
          原代码：Company.joins(:votes).where("companies.is_hidden is false").order("votes.updated_at DESC").uniq
          修改过的代码：Company.joins(:votes).select("companies.*, votes.updated_at").where("companies.is_hidden is false").uniq.order("votes.updated_at DESC")
        6.比group_by更有效率的方法。旧方法:Tag.all.group_by(&:tag_type).keys.新的方法:Tag.select(:tag_type).distinct.map(&:tag_type)。测试1500+个tag。group_by花费大约6ms，然而select只需要1ms.
        7.controller的命名空间问题.
          1).生成controller: rails g controller admin/tags
            class Admin::TagsController < ApplicationController 
              def show 
                @tag = Tag.find(params[:id])
              end 
            end
           2).routes相关
             A).http://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html;
             B).match "/tags/(:id)" => "admin/tags#show", as: :show_tag, via: [:get] # 生成"/tags/test/show"，不会包含admin的前缀
        8.has_and_belongs_to_many中正确删除方法:@user.tags.delete(Tag.find(tag_params[:id])。这样就不会删除tag而只会删除users_tags中对应的record
        9.去除数组中的空内容，nil元素。[12, "12", "", nil].reject(&:blank?) # => [12, "12"]
        10.ckedit自定义toolbar的图标
        inline javascript code of view
        	CKEDITOR.replaceAll(function(ta, config){
        		if(ta.className.indexOf("custom-ckeditor") >= 0) {
        			config.customConfig = "/javascripts/custom_ckeditor_config.js";
        		} else if(ta.className.indexOf("custom-survey-ckeditor") >= 0) {
        			config.customConfig = "/javascripts/custom_survey_ckeditor_config.js";
        		}
        	})
        /javascripts/custom_ckeditor_config.js
        CKEDITOR.editorConfig = function( config ) {
        	config.toolbar = [
        		{ name: 'editing', groups: [ 'find', 'selection', 'spellchecker' ], items: [ 'Find', 'Replace', '-', 'SelectAll', '-', 'Scayt' ] }
        	];
        	config.language = 'en';
        }
        11.nest models includes
        	Tag.includes(:articles).includes(custom_pages: {sub_menu_items: :menu_item}).references(:custom_pages).where("menu_items.id = ?", @section.id)
SECTION2 - System 
	1.生成8位随机密码: openssl rand -base64 8
        2.在Mac OSX上根据端口号查询进程: lsof -n -i4TCP:8090 | grep LISTEN
        3.Benchmark of ubunut
        	1) wget https://freevps.us/downloads/bench.sh -O - -o /dev/null|bash #主要测试下载速度
        	2) https://github.com/kdlucas/byte-unixbench.git ＃更加详细的信息
        4.ln的使用方法
        	1).创建 -> ln -s {/path/to/file-name} {link-name}
		2).更新 -> ln -sfn {/path/to/file-name} {link-name}
		3).删除 -> rm {link-name}
        5.删除未知的ssh登录的用户
        	ps aux | egrep "sshd: [a-zA-Z]+@" 
        	kill [-9] PID
        6.rsync同步文件
        	rsync -r --partial --progress --rsh=ssh REMOTE_IP:SOURCE_DIR DIST_DIR
SECTION3 - Database(Postgresql)
	1.将一个数据库中的表的数据导入到另一个数据库: pg_dump -t tablename dbname | psql otherdbname
	2.进入到postgres数据库的console: psql dbname username(\d 查看所有表,\d tablename 查看表结构)
        3.查看表articles_tags中的index的方法: \d articles_tags;
        4.删除表custom_pages中的某个字段sub_menu_item_id
        	ALTER TABLE custom_pages DROP COLUMN sub_menu_item_id;
SECTION4 - Server
	1.502 bad gateway 分别查看: /production_dir/log/thin.log /var/log/monit.log
SECTION5 - VIM
        1.Movement
          Ctrl-D  move half-page down
          Ctrl-U  move half-page up
          Ctrl-B  page up
          Ctrl-F  page down