rod mclaughlin

Class variables in Ruby on Rails (05 may 09)

Rails has a cute method, cattr_accessor, which creates class-wide variables

These variables begin with '@@' and are for storing things you only need one of across your whole application

My http://pdxspurs.com has a 'News' section which uses the Guardian Ruby API to search the files of the Guardian newspaper in London for news about football - http://www.guardian.co.uk/open-platform

It takes a while to search, and the news doesn't change very often, so I wanted to set it up so the news is only gotten once per day

I store the date, and if the date has changed since the last time anyone looked at the news, I get new news

The funny thing is, it didn't work in development - it always reloaded the news, even if the date hadn't changed

I figured out why - all code is reloaded in development mode every time you hit 'Reload' in your browser

This means that the class-wide variables were reset, so the code thought the date was new every time

So I ran it in production mode, and t worked - it only loaded the news once

I guess I'll have to wait 'til tomorrow to find out if it really worked, but here's the code, guardian.rb:

# Part of the Guardian API
require 'custodian'
# sudo gem install libxml-ruby
require 'xml/libxml'

class Guardian
  ONE_DAY = 60 * 60 * 24
  NUM_DAYS_BACK = 4
  HEAD = "//content/headline"
  BODY = "//content/type-specific/body"
  DATE = "//content/publication-date"
  ENDING = "\n</content>"
  MAX_RESULTS = '25'
   
  cattr_accessor :results
# Create @@results and @@last_time_got
  cattr_accessor :last_time_got
  
  # Formats date num_days ago: 'Sun Oct 05 11:00 2008' -> '20081005'
  def Guardian.display_date(num_days)
    t = Time.now - (num_days * ONE_DAY)
    d = t.to_s
    l = d.length
    y = d[l-4..l-1]
    d = d[8..9]
    m = t.month.to_s
    m = '0' + m if m.length < 2
    y + m + d
  end
  
  def Guardian.result(which_one)
    Guardian.set_results
    which_one = rand(@@results.length) if which_one.nil?
    return @@results[which_one.to_i]
  end

  def Guardian.results_html
    Guardian.set_results
    return 'No news is good news' if @@results.length < 1
    html = ''
    i = 0
    @@results.each do |r|
      arr = r.split("\n")
      tit = arr[0]
      tit.gsub!('&nbsp;', '')
      html += "<a href='" + "/news/" + i.to_s + "'>" + tit + "</a>" + "\n<br/>"
      i = i + 1
    end  
    return html
  end

private
  def Guardian.set_results    
    
    Custodian.api_key = 'THIS IS A SECRET'

    @@last_time_got = 'nil' if @@last_time_got.nil?

    @date = Guardian.display_date( NUM_DAYS_BACK )   
    @@results = [] if @@results.nil?
  # Get new results just once every day
    return if @@results.length > 1 and @date == @@last_time_got       
    @@last_time_got = @date
    
    @articles = Custodian::Article.find(:all,
        { :q => "Tottenham", :filter => '/football',
          :after => @date, :content_type => 'article', 
          :count => MAX_RESULTS })
    if @articles.length < 1
      @@results = ["Well, they say no news is good news"]
      return
    end

    @@results = []
    xml_str = ''
    @articles.reverse.each do |a|  
      begin
  # Correct the XML
        xml_str = a.xml.to_s
        xml_arr = xml_str.split("\n")
  # Strip off the Grauniad's incorrect ending - '</publication-date>...</content>'
        xml_arr.delete_at(xml_arr.length - 1)
        xml_str = xml_arr.join("\n")
  # Tack on the happy ending
        xml_str = xml_str + ENDING
        doc = XML::Parser.string( xml_str ).parse
        date = ''
        head = ''
        body = ''
        doc.find(HEAD).each do |node|
          head = node.content
          head = "<b>" + head + "</b>"
        end
        doc.find(DATE).each do |node|
          date = node.content
          date = "\n<br/><b>" + date[0..9] + "</b>"
        end
        doc.find(BODY).each do |node|
          body = node.content 
  # Try to add some formatting
          body.gsub!( ".  ", ".\n<br/><br/>")     
        end
        @@results << head + date + "\n<br/><br/>" + body if not (body.strip.empty?)

      rescue Exception => err
        @@results = [err.message]     
      end
    end
  end

end

Portland

London