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Move Over Rails. Here Comes Merb. : Page 3

Merb is potentially much faster than Rails, and the combination of Merb and Ruby can provide the performance most web apps require. Find out how Merb can deliver a 2-4X speed increase over Rails and why that makes it better for certain applications.


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Using DataMapper and a Database for Rendered Feed Data
To read all of the seed RSS URLs and fetch the RSS feed XML for each seed RSS URL, I created a model class FeedDataManager that reads the feed_sources database table using the DataMapper-generated class FeedSource. You can look at the source file app/models/feed_data_manager.rb for the full implementation, but the following few code snippets show how you fetch and process RSS data:

feed_sources = FeedSource.all.collect {|f| f.url} feed_sources.each {|source| puts "\n* * processing #{source}" begin rss = SimpleRSS.parse(open(source)) rss.items.each {|item| puts " link: #{item.link} title: #{item.title} feed title: #{rss.feed.title}" # item.context # all content text # save data to database feed = Feed.new feed.url = item.link feed.title = item.title feed.content = item.content feed.feed_name = rss.feed.title feed.posted_date = Time.now feed.save! puts "* saved #{feed}" } rescue print "Error: #{$!}" end }

Running this periodically in the background, the ideal implementation, is relatively easy. Merb has built-in support for running background tasks from controllers, but I wanted to do something different: start a work thread as soon as all application code has loaded. To do this, I edited the config/init.rb file by adding a statement to the run after loading block:



Merb::BootLoader.after_app_loads do # This will get executed after your app's classes have been loaded. DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/dev.db") # Start up the background work thread: Thread.new { FeedDataManager.new } end

The initialize method for class FeedDataManager never returns. Rather, it initializes instance data and enters a long loop that fetches feeds, and then the thread sleeps for five hours before re-fetching the feeds.

Now you need a controller to get the feed data for a view (note that I have removed the unnecessary controller methods that merb-gen resource feeds ... created):

class Feeds < Application # provides :xml, :yaml, :js ## do not need to handle web service clients def index @feeds = Feed.all display @feeds ## make available to the view end end

My initial edits for the app/views/feeds/index.html.erb were:

<h1>Latest Ruby Blog Entries</h1> <% @feeds.each {|feed| %> <h4> <%= feed.title %> </h4> <a href="<%=feed.url%>" target="new">link</a> <%= feed.content[0..70]%> <br/><br/> <% } %>

Finally, before running the first implementation, I wanted to set the method index in the controller class Feeds to be the default route for the web application in config/router.rb:

match('/').to(:controller => 'feeds', :action =>'index')

That is pretty much bare bones, but you now have a complete web application (that you will improve) for fetching feeds and displaying them.

One thing that surprised me when I first ran this prototype was its speed. It was fast without caching and despite database fetches for the data it would display. I ran the Apache Benchmark utility and discovered that this prototype provided 44 page renders per second on my MacBook:

ab -n 5 http://localhost:4000/

The next section explains how you can change the design of the demo application to incorporate in-memory storage.



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