When I wrote about the Dual
Schema
problem a few weeks ago, I specifically wrote that the
Rails model is backwards because it
derives the in-memory schema from the database schema. While I still
believe that, Rails’
ActiveRecord::Migration library
does make it significantly easier to manage the database from Ruby code.
For those not familiar, ActiveRecord::Migration is a series of Ruby
script files that define the database schema. Inside each migration
script is an up and down method, so you can migrate forward and backward
in the history of your project. And it provides easy to use abstractions
such as create_table and add_column so you don’t have to geek out on
SQL syntax (unless you want to). Once you have a collection of these
scripts, simply calling rake migrate will bring your database instance
up to the current schema
(rake is Ruby’s equivalent
of make). Or, you can set your database to a specific version of the
schema by running rake migrate VERSION=X.
I wonder why the Rolling on Rails tutorial uses the database tools directly instead of ActiveRecord::Migrate? I’m thinking it wasn’t available when the tutorial was written. Whatever the reason, they really should update the tutorial to reflect the current state of Rails.
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