Some Random Blog

On my latest project, I discovered I had to pre-populate the project's database with existing content. Jon Udell just posted about how much of a waste of time this can be in some circumstances, but in this case, Hpricot and database migrations made it easy. This wouldn't be a solution I'd use if I needed the data as anything beyond a one-off bootstrap, but in this case it worked really well.

Hpricot, for those who don't know, is an HTML parser for Ruby that's fun to use. When I was first learning Ruby, most of the simplest yet useful projects I could come up with used Hpricot to grab content off of websites and format or combine it in different ways. Its syntax looks like this:

require 'hpricot'
require 'open-uri'

uri = URI.parse(link)
doc = Hpricot(open(uri))

name = (doc/"li.active a").inner_html
page_title = (doc/"title").inner_html
body = (doc/"#content_body").html

In this example, Hpricot is using CSS selectors to grab different pieces of content out of the page in link. The nice thing about using CSS selectors here is the code tends to be less fragile than screenscrapers that depend on the architecture of the page.

Page scraping can be a frustrating art, especially if the page layout changes or if pages are inconsistent, or have unique properties. Luckily, in this case, I only had to get it right once, and even then, I didn't have to get it completely right. I used this four-stage process:

1. Use Hpricot to get as much data off the page and into our data structures as possible.
2. Persist this data to the database, and make appropriate changes that Hpricot missed, or couldn't catch.
3. Dump the database to a file, and use it to bootstrap our production database.
4. Repeat until finished.

Rails database migrations made this relatively easy. I ended up with three migrations. The first migration created the structure of the database. The second loaded the current page data dump from the dump file. The third grabbed a few pages I still needed to parse, and I was left with data that I could tweak and dump, overwriting it with a dump containing all the page data (including the stuff I just tweaked). I could then blow away the database and repeat until I didn't have any more pages to parse.

This worked perfectly, since I didn't have to spend time getting my Hpricot parsing perfect (since I could modify the resulting data using our CMS and re-dump), and I was left with a dump of all the data that I needed in order to dynamically generate these formerly mostly static pages.

This article made it across my RSS reader today. I ran into my own problem with this while writing a custom CMS for work. We wanted to have reusable components that could be added to CMS pages, which could take various parameters, could be cached, and could be viewed in different ways given a size. I investigated Rails components at work, but noticed that using those is discouraged by the Rails community.

My investigation brought me to Typo’s sidebar model, which I used as the basis for the model we ended up using for the prototype of the project. The ultra-simplified version of the model works like this:

We have a Sidebar base class, which inherits from ActiveRecord::Base. Sidebars inherit from this Sidebar class.

Which gives us something like this:

class Sidebar < ActiveRecord::Base
  serialize :config

  class << self

    def params
       @params ||= []
    end

    def param(name, type, options = {})
      params << options.merge({:name => name, :type => type})
      self.send(:define_method, name) do 
        self.config[name] || options[:default]
      end
      self.send(:define_method, "#{name}=") do |value|
        self.config[name] = value
      end
    end
  end
end

class StaticTextSidebar < Sidebar
  param :content, :text, :default => "Hello, World!"
end

So now we have a way of defining sidebars and their parameters. The metaprogramming in the Sidebar base class allows us to programatically query the parameters declared in a Sidebar. This will be important later. For now, we still need to declare the view of a sidebar, so we do it in _static_text_sidebar.rhtml:

<%= sidebar.content %>

Now, we add a helper to application_helper.rb to render the sidebar:

def render_sidebar(sidebar)
  render :partial => sidebar.class.name.underscore, :locals => { :sidebar => sidebar }
end

and then we can call render_sidebar in any of our views on an instance of a sidebar to render it. It’s not perfect, but it’s good enough for a prototype!

From here, we have a very basic reusable model-view framework that we can include in any of our pages. Sidebar instances can be associated with content on a page to be displayed, and their configuration can be serialized to the database along with the items they display with.

Creating and configuring sidebars can be done programmatically, by generating a form based on the parameters a sidebar takes and placing that form data into the sidebar, the same way one would with a standard ActiveRecord object. Their parameters can be validated using standard Rails validations and the result of the render_sidebar call can be cached.

This basic idea, with a little bit of work, can easily form the basis for a simple reusable component architecture, and we’ve been having a ton of success with it so far.

Jeff Atwood's Coding Horror has recently become one of my favorite blogs (although he seems to be more of a Code Complete guy while I'm more of a Pragmatic Programmer guy).

One of the recent posts on the blog made the point that "the best code is no code at all." This is something I completely agree with, but I get into arguments on this topic pretty regularly. This particularly comes up when I discuss static vs. dynamic languages. When I talk about Ruby being my favorite language (for now), many people who come from a C++/C#/Java mindset wonder how correct the code I write can be if the compiler isn't doing any compile-time checks. After all, errors are much cheaper to catch early, and compile-time checking is really early, right?

In theory, they have a point, but in practice, it hasn't been a problem. I was thinking about this recently, and I think there are two main reasons I haven't had noticeably more bugs in my dynamic programs than I do in my static programs:

The first is what Jeff refers to in his blog: Dynamic languages, as a whole, require less code to be written. I don't care how "correct" the compiler thinks my code is, I am smart enough (in a way) to write broken code that the compiler can't catch. When the broken code is a single line hidden in a ton of boilerplate C++/C#/Java style class/method/etc. definitions, it takes a little longer for me to wrap my head around what I need to do to fix the problems. In Ruby, I find that my mistakes are much easier to catch and fix, because my code _is_ my intent. Part of it is because less code = less room to make mistakes, and the other part is less code = easier to find the mistakes I do make.

The other reason, which branches off from the first, is that the dynamic programs are (again, in my experience) easier to test. When you can torture every object in the system at runtime, it becomes unbelievably easier to mock, isolate, and test the exact functionality that exists in a part of the program. Not only does this hit most of the dumb mistakes that compile-time checks will notify you about, it also will tell you when another dumb mistake breaks logic errors that the compiler could never tell you about.

This leads me to an interesting fact that I just recently discovered: Not only does the code I write in C++/C# not have fewer (discovered) errors than my Ruby code, my Ruby code is, on the whole, easier to fix when things do go wrong. Less code provides a lot of benefits when it comes to agility, avoiding needless multitasking, and verifying code correctness, and that's one of the many reasons I've been moving much more toward more dynamic languages lately (and been much a much happier developer for it).