PragDave

Debugging with Ruby

Thanks to Ed Burnette for this link.

Rails and the Legacy World

I gave what turned out to be a slightly controversial keynote at RailsConf. In it, I pointed out that people (like me) who can use Rails on green-field projects are incredibly privileged. We get to code using cool technologies in an incredibly agile, reactive environment, producing applications that just work.

But, at the same time, there are a whole lot of people who don’t get to enjoy the world of Rails.

Migrations Outside Rails

I’m about 3 weeks into the rewrite of the Active Record chapters for the new Rails book. In the book, I try to demonstrate Active Record with real, live code. At the same time, I don’t want to run every single piece of code in the context of a Web application. So, I use Active Record stand-alone, without having the rest of Rails loaded. All my demonstration files start:

    require "rubygems"
    require_gem "activerecord"

and then include a call to establish_connection to connect to the database.

At this point, I’m up and running, and I can play with all the Active Record functionality. But… I still wanted to create tables in the underlying database. In the first edition, I used DDL to do this, but in the second I wanted to use migrations.

My first hack was to use the fact that the various schema definition methods are defined both for migrations and in every database connection object. That let me use the following in my code:

    ActiveRecord::Base.connection.instance_eval do
      create_table children, :force => true do |t|
        t.column :parent_id, :integer
        t.column :name,      :string
        t.column :position,  :integer
      end
    end

I was pretty chuffed with this until Jamis Buck (who else) pointed out a more elegant way:

    ActiveRecord::Schema.define do
      create_table children, :force => true do |t|
        t.column :parent_id, :integer
        t.column :name,      :string
        t.column :position,  :integer
      end
    end

As I see more and more people start to use Ruby (and Active Record) as enterprise glue, being able to bring these kinds of Rails goodies to non-Rails applications is a win all around.

Decimal Support in Rails

A couple of blog posts ago, I commented on the dangers of converting database decimal columns into Ruby floats. And, five months early, Santa delivers. In the Rails trunk, numeric and decimal database columns with a scale factor are now converted into Ruby BigDecimal objects. If the scale factor is zero, they instead become integers.

Migrations now support decimal columns too, with the addition of two new attributes, precision and scale.

   add_column :orders, :price,
              :decimal, :precision => 8, :scale => 2

I just spent a day reworking all the Depot chapters to use this, and it seems to work great. (And, no, the updated PDF isn’t released yet. I’m also half-way thought the ActiveRecord chapter rewrite, and need to get that finished before the next release.)

I’d be interested to hear[1] from folks currently using BigDecimal for financial calculations. Is there a preferred rounding mode? Any gotchas?

In the meantime, thanks core team.

1. dave∂pragprog.com

Pluvo

LtU has a link to Pluvo, a language which seems like a cross between Python, JavaScript, Ruby, and Lisp. It has some interesting ideas (coordination is a fun one) and the basic system (written in Python) is currently less than 50k to download.