miceda

The Problem

Your trying to deploy a Rails app using Deprec on Ubuntu running behind a proxy server and getting connection errors.

Possible solution

You need to tell apt-get about your proxy server. Here’s how I did it:

1. Create a file ”/etc/apt/apt.conf”
2. In the file add the following:

Acquire { Retries "0"; HTTP {Proxy "http://YOURPROXY:PORT";};};

Now edit the proxy information in ”/etc/wgetrc” by uncommenting “use_proxy” and setting “http_proxy”:

use_proxy = on
http_proxy = http://YOURPROXY:POST

Finally add the proxy to ”/etc/bash.bashrc”

http_proxy = http://YOURPROXY:POST
export http_proxy

Once I did this, everything worked great!

Here’s a quick snippet on how to install and create a ShapeFile from data in your Model.

The setup

1. Download and Install ShapeLib. Make sure to note where the install puts the libshp.so and the shapefil.h (you may need that information later).
2. Download ruby-shapelib
3. Unzip ruby-shapelib and run: “ruby ./extconfig.rb”. Depending where step 1 put your files,you made to alter some options you pass to this program. Specifically—with-shapelib-dir and—with-shapelib-include
4. Once you’ve done that, make sure everything is working right with irb:

$ irb
>> require 'shapelib'
=> true

If you get “true”, you’re good to go.

Simple example

Let’s say we have a table called markers, with the fields lat (float), lng (float), and created_at (datetime). We want to create a shapefile for the points and also collect the time (created_at) as an attribute in the shapefile.

require 'shapelib'

# Create a shapefile from an array of markers
def make_shapefile(markers)
  # Create the shapefile.
  # First argument: is the name of the file to create
  # Second: The shapefile type
  # Third: An array of array(s) describing the attribute (name, type, size)
  fp = ShapeLib::ShapeFile::new("test1.shp",:Point, [['date', :String, 32]])

  # Loop over the markers
  markers.each do |m|
    point = ShapeLib::Point::new(m.lng,m.lat,{"date" => m.created_at})
    fp.write point
  end

  fp.close
end

# try it out...
make_shapefile( Marker.find(:all) )

If all is working right, you should end up with 3 files: test1.shp, test1.shx, and test1.dbf

If you don’t have one already, here’s a nice open-source application to tinker with your new shapefiles: qgis

Here’s a little script I use to scrape archived pages from the Alexa Wayback Machine . Basically, it works like this:

1. Query Alexa for an old URL you’re looking for and the Years you’re interested in
2. Use Hpricot to look in the results for links to archived pages. The pattern is http://web.archive.org/web/200301../url. Where the number is the timestamp and the url on the end is the old page you’re looking for. Return and array of successful matches
3. Loop over the results of above and download the pages locally using curl (you could also use wget)
4. Save the pages with the name “archive_timestamp.html”

Here’s the code:

require 'hpricot'
require 'open-uri'

urls = %w[http://sample.com http://sample2.com ...]
years = %w[2002 2003 2004]

# Search Alexa for the following URLS and Years
# extract the relevent links from the search result pages
def extract_links_from_search(search_urls=[],years=[])
  results = []
  search_urls.each do |u|
    years.each do |y|
      search_alexa = "http://web.archive.org/web/#{y}*/#{u}"
      doc = Hpricot(open(search_alexa))
      (doc/:a).each do |link|
        ul = link.attributes['href']
        # Search result pages have the following url, followed
        # by the timestamp (20030313094512)
        # followed by the search url
        if ul =~ /http://web.archive.org/web/d+/http:/
          results << ul
        end
      end
    end
  end
  results
end

def download_and_store_pages(results=[])
  results.each do |url|
    #Create a file name based on the Timestamp
    fn =  "archive_#{$&}.html" if url =~ /d+/
    puts "Saving as: #{fn}"
    `curl #{url} -o #{fn}`
  end
end

outp = extract_links_from_search(urls,years)
puts "Getting the data"
download_and_store_pages(outp)

This is quick and dirty and took about 10 minutes to write. It could probably be simplified, but it does the job for me.

So your app needs to generate XML. No problem, ActiveRecord gives you it for free. Simply call mymodel.to_xml and your done. But what happens if you need to generate more complicated…specialized XML? There are a few options:

1. Don’t call to_xml, generate the XML using a template (.rxml)
2. Override the to_xml method. As mentioned in the docs
3. Create a separate method for generating the XML

To keep things simple, and for reasons we’ll see later, let’s use 3.

The example

Ok. I have a model, Car, with 3 attributes (year,make,model). Here’s what the default XML looks like:

car = Car.find(:first)
car.to_xml
=>

<car>
 <make>Nissan</make>
 <model>Pickup</make>
 <year>1995</year>
</car>

So let’s customize the XML to add a namespace for the elements and change the tag type. In the Car model we’ll create a new method called my_xml instead of overriding to_xml:

def my_xml(options={})
  options[:indent] ||= 2
  xml = options[:builder] ||= Builder::XmlMarkup.new(:indent => options[:indent])
  xml.instruct! unless options[:skip_instruct]
  xml.mycar(:Vehicle, "xmlns:mycar" => "http://crazystuff.org/car/ns") do
    xml.mycar(:make, self.make)
    xml.mycar(:model, self.model)
    xml.mycar(:year, self.year)
  end
end

The Model uses the Builder library for creating the XML. That was easy. Now when I call car.my_xml I get this:

<?xml version="1.0" encoding="UTF-8"?>
<mycar:Vehicle xmlns:mycar="http://crazystuff.org/car/ns">
  <mycar:make>Nissan</mycar:make>
  <mycar:model>Pickup</mycar:model>
  <mycar:year>1995</mycar:year>
</mycar:Vehicle>

Perfect! Now let’s try and query all Cars and see what we get:

all_cars = Car.find(:all)
all_cars.to_xml
=>
NoMethodError: undefined method 'my_xml_' for #<Array:0x1379810>

What the *$%@! That’s not right. Calling Car.find(:all) returns an Array. Array doesn’t have a method my_xml.

But how does Rails do it? If “all_cars” is an Array, then Array within Rails must support the to_xml method. As it turns out Rails adds some tricks to some of the core pieces of the Ruby language. Of interest to us right now is the module ActiveSupport::CoreExtensions::Array::Conversions. It defines a to_xml method that is a mixin for the Array class.

We could open up the Module and change it. Or we could just create our own method and include it into Array. Let’s do something like that:

module MyConversion
  def my_xml
    options[:builder]  ||= Builder::XmlMarkup.new(:indent => options[:indent])
    # TODO: Move the xmlns from Vehicle to here...
    options[:builder].tag!("mycar:AllVehicles") do
      # Here's we loop over each entry (model) and call it's my_xml
      each { |e| e.my_xml(options.merge!({ :skip_instruct => true })) }
    end
  end
end

# Don't forget to do this!
class Array
  include MyConversion
end

Ok. That’s it. Now when we call my_xml regardless of whether it’s a Array or a single object it works as expected.

Have a look around in the ActiveSupport Core Ext. There’s a lot to learn there.

If you find yourself in the nasty position of having to use Oracle with Ruby, watch out for a problem related to unsupported datatypes. Specifically these types:

• SQLT_TIMESTAMP
• BINARY_DOUBLE
• BINARY_FLOAT

However, I found a little quick fix that seems to work. Add this to your code:

require 'oci8'

# handle the timestamp mapping
OCI8::BindType::Mapping[OCI8::SQLT_TIMESTAMP] =
OCI8::BindType::OraDate

# handle the binary_float
OCI8::BindType::Mapping[100] = OCI8::BindType::Float

# handle the binary_double
OCI8::BindType::Mapping[101] = OCI8::BindType::Float

The good news is it looks like the fix will be in the next release of OCI8.

As you know, the default Gem server included with RubyGems runs with WEBrick. I wanted something a little quicker and more reliable. So, here it is: mongrel_gem_server. Nothing complicated. Just the original Gem server adapted to use Mongrel.

if defined? “what does it mean?!”

Plowing through various Rails and Ruby source code, I keep running across the method defined?. However, a quick look though the API turned up nothing on it. Where’s it coming from? I can’t find it in Module, Kernel, or Object…time to explore! A quick Google search shows RedHanded solved this mystery way back in 2004.

As it turns out defined? lives in eval.c. The logic responsible for defined? actually has the identity is_defined starting around line 2249. As Redhanded explains: “defined? takes its argument and simply queries the symbol table to see if it is defined. If it is, you get a simple string of identification”:

$ x = 10
=> 10
$ defined? x
=> "local-variable"
$ def hello; puts "Hello" end
$ defined? hello
=> "method"
$ class Test; end
$ defined? Test
=>"constant"

Examples of use

Since I haven’t had the opportunity to use it yet, Here’s a couple examples I’ve found:

In Rails initializer.rb uses it to test for the existence of a constant:

   def initialize_logger
     return if defined?(RAILS_DEFAULT_LOGGER)

The method real_connect in mysql.rb uses it to check UNIXSocket:

 if (host == nil or host == "localhost")
    and defined? UNIXSocket then ...

Cliff notes version

1. defined? is classified as an operator not a method
2. defined? returns nil if the argument passed to it is NOT defined
3. defined? returns a string identification of the argument passed as defined in the symbol table

Now, I wonder where and how the method is_defined is translated into the operator defined?

Just a simple problem

It all started when I wanted to add the Rails default logger to some code I was working on. The code sits in the lib directory and I wanted to use the same logger the controllers and models use. Without thinking I threw a call to logger.info(”whatever”) in my code. Obviously that’s not going to work as I quickly got an error. Fortunately a quick google search turned up this. Basically to use the logger in my code I simply needed to call the constant RAILS_DEFAULT_LOGGER. Ok, great. Problem solved. Time to move on. But something caught my curiosity. How is Rails setting this constant and making it available to my Class ?

The plot thickens

So I decide to dig in. Luckily I start by looking at the code in initializer.rb. Rails::Initializer is called when your app boots up. It does most of the heavy lifting configuring the environment for Rails. Right around line 258, I find the answer to the constant mystery:

  Object.const_set "RAILS_DEFAULT_LOGGER", logger

Great. Ok now I can move on…but what the heck is

  Object.const_set

An aha moment

As it turns out the method const_set allows you to set a constant on the given object. In our case we’re setting the constant on Object - the parent of all classes in Ruby. So let’s see how this works…fire-up IRB and follow along:

Let’s start by seeing what constants Object already has. Ruby makes that easy:

  > Object.constants

As you can see (in your IRB terminal) Object comes with a large list of constants already. Ok let’s add our own

  > Object.const_set("WHOS_THE_MAN", "DAVE_IS")
  > Object.constants

Wow, you just added a constant to the supreme Ruby Object. Next, let’s see how we can get to this in our own classes:

  class Test
    def whos_the_man?
      puts WHOS_THE_MAN
    end
  end
  t = Test.new
  t.whos_the_man => DAVE_IS

So there you have it. A clever way to add constants that are available throughout your Ruby app. Of course you’re not limited to just adding to Object. Your Class can have it’s own constants that are scoped to it and its subclasses. You gotta love this language!