Book.where(:title => 'Tale of Two Cities').first_or_create

Book.where(:title => 'Tale of Two Cities').first_or_create do |book|
  book.author = 'Charles Dickens'
  book.published_year = 1859
end

Book.where(:title => 'Tale of Two Cities').first_or_initialize

MongoDB会消耗太多的磁盘空间了。当然了，这与它的编码方式有关，因为MongoDB会通过预分配大文件空间来避免磁盘碎片问题。它的工作方式是这样的：在创建数据库时，系统会创建一个名为[db name].0的文件，当该文件有一半以上被使用时，系统会再次创建一个名为[db name].1的文件，该文件的大小是方才的两倍。这个情况会持续不断的发生，因此256、512、1024、2048大小的文件会被写到磁盘上。最后，再次创建文件时大小都将为2048Mb。如果存储空间是项目的一个限制，那么你必须要考虑这个情况。该问题有个商业解决方案，名字叫做TokuMX，使用后存储消耗将会减少90%。此外，从长远来看，repairDatabase与compact命令也会在一定程度上帮到你。

MongoDB中数据复制的复制集策略非常棒，很容易配置并且使用起来确实不错。但如果集群的节点有12个以上，那么你就会遇到问题。MongoDB中的复制集有12个节点的限制，这里是问题的描述，你可以追踪这个问题看看是否已经被解决了。

尽管已经不建议被使用了，不过MongoDB还是提供了另外一种复制策略，即主从复制。它解决了12个节点限制问题，不过却产生了新的问题：如果需要改变集群的主节点，那么你必须得手工完成。

MongoDB的32位版本也是不建议被使用的，因为你只能处理2GB大小的数据。

这对于初学者来说依然是个让人头疼的问题，MongoDB的管理控制台太差劲了。我所知道的最好的工具是RoboMongo，它对于那些初次使用的开发者来说非常趁手。

cd [my project dir]
svn import -m "First Check-in" [SubversionRunningMachine]/[ProjectName]/[my project dir]
cd ..
svn co [SubversionRunningMachine]/[ProjectName]/[my project dir] [my project dir]

1，编码设置是否一致，也即是你项目原来的编码和现在eclipse用的默认编码是否一致

2，导入项目中jar路径可能已经被改变，多数情况下都是这个原因造成，我也曾经遇见过，你要确保你的jar包路径都没问题。myeclipse有查看jar路径的视图你可切换看看，报红X的就都是路径被改动过的，重新加进来就OK。

3，在problem控制台里有如下错误提示：Java compiler level does not match the version of the installed Java project facet。这种情况一般可以在项目上右键-->properties-->然后找到project facets和 Java Compiler两个选项，修改其使用的jdk版本即可。

# encoding: utf-8
require 'rubygems'
require 'nokogiri'
require 'open-uri'

class Zongheng

  def self.start
    urls = {
      "不败战神" => "http://book.zongheng.com/showchapter/251393.html"
    }
    start_time = Time.now.to_s
    begin
      urls.each_pair do |name, val|  
        get_chapter_list(name,val)
      end
    rescue Exception => e
      Rails.logger.error "fetch zongheng had a Exception"+e.to_s
    end
    Rails.logger.info "Zongheng end>>>>start_time="+start_time+">>>>end_time="+Time.now.to_s
  end

  def self.get_chapter_list name,base_url
    f = i_open base_url
    return "" unless f
    titles = Nokogiri::HTML(f).css("div.booklist td a")
    titles[-2..-1].each do |title|
      post_content = get_post_content title['href']
      if post_content && post_content.length>100
        # 有内容  则入库，标题，章节内容，小说名，
        novel = Novel.where(:name => name).first_or_create
        chapter = Chapter.where(:name => title.text).first_or_create(:content => post_content,:novel => novel)
        if post_content.length != chapter.content.length
          chapter.content = post_content
          chapter.save
        end
      end
    end
  end

  def self.get_post_content url
    # p url
    f = i_open url
    return "" unless f
    post_content = Nokogiri::HTML(f).css("#chapterContent");
    # 去掉无用链接
    post_content.css(".watermark").remove
    post_content.css("a").remove
    post_content.inner_html.encode("utf-8")
  end

  def self.i_open url
    begin
      open(url,:read_timeout=>20)
    rescue Exception => e
      return nil
    end
  end

end

def geekify(string)
  string.gsub(/[leto]/, 'l' => '1', 'e' => '3', 't' => '7', 'o' => '0')
end

geekify('leet') # => '1337'
geekify('noob') # => 'n00b'

def doctorize(string)
  string.gsub(/M(iste)?r/, 'Mister' => 'Doctor', 'Mr' => 'Dr')
end

doctorize('Mister Freeze') # => 'Doctor Freeze'
doctorize('Mr Smith')   # => 'Dr Smith'

# Index HTML Files
if (-f $document_root/cache/$uri/index.html) {
  rewrite (.*) /caches/$1/index.html break;
}

# HTML Files
if (-f $document_root/cache/$uri.html) {
  rewrite (.*) /caches/$1.html break;
}

# Catch all
if (-f $document_root/cache/$uri) {
  rewrite (.*) /caches/$1 break;
}

class Object 
  def tap 
    yield self 
    self 
  end 
end

blah.sort.grep( /foo/ ).map { |x| x.blah }

xs = blah.sort.grep( /foo/ )
p xs

# do whatever we had been doing with the original expression
xs.map { |x| x.blah }

blah.sort.grep( /foo/ ).tap { |xs| p xs }.map { |x| x.blah }

def index
  @recipe_collection = RecipeCollection.from_params(params)
  render json: @recipe_collection.recipes
end

class RecipeCollection
  attr_accessor :featured, :time_filter

  # Handles the logic of sorting params into a collection
  def self.from_params(params)
    RecipeCollection.new.tap do |recipe_collection|
      recipe_collection.time_filter = params[:time_filter]
      recipe_collection.featured = params[:featured]
    end
  end

  # Should return an ActiveRecord relation
  def recipes
    query = Recipe.scoped
    query.featured if featured.present?
    query.filter_by_time(time_filter)
  end

  def time_filter
  valid_time_filters.include?( @time_filter ) ? @time_filter : default_time_filter
  end

  def default_time_filter
    "today"
  end

  def valid_time_filters
    %w[ today yesterday this-week this-year ]
  end
end

<%- if current_user.redesign_enabled? %>
  <%# new code %>
<%- else %>
  <%# old code %>
<%- end %>

class ApplicationController < ActionController::Base
  before_filter :add_view_path_for_redesign

  private

  def add_view_path_for_redesign
    if current_user.redesign_enabled?
      prepend_view_path Rails.root.join('app/views/redesign')
    end
  end
end

# original
app/views/users/edit.html.erb
app/views/users/show.html.erb

# redesign
app/views/redesign/users/edit.html.erb
app/views/redesign/users/show.html.erb