Saturday, July 11, 2009

Rails Fixtures and Seed Data

One of the things that makes Ruby on Rails a great web framework is the quantity of tools available that are focused around the task of making web applications easy to build and encourage good software engineering practices.

Rails makes it really easy to test by building in a testing framework. One aspect of this is what are called "fixtures", data described in CSV or YML formats that is loaded into the database for each round of testing.  Tests live at both the unit (model) and integration (controller) level. End to end tests that involve the view are traditionally run from an automated tool, such as Selenium or HPQC (ha).

UPDATE ALERT... Rails 2.3.4 has a nice, new way to do this.

Fixtures also make it easy to load seed data into the database.  You can do this with migrations, but it gets messy, especially if you use ActiveRecord to do it, and then you delete a model class sometime in the future, it forces you to do an edit of an old migration, which means you might as well roll them all up. I prefer:

rake db:fixtures:load
Which runs:
namespace :fixtures do
    desc "Load fixtures into the current environment's database.  Load specific fixtures using FIXTURES=x,y"
    task :load => :environment do
      require 'active_record/fixtures'
      (ENV['FIXTURES'] ? ENV['FIXTURES'].split(/,/) : Dir.glob(File.join(RAILS_ROOT, 'test', 'fixtures', '*.{yml,csv}'))).each do |fixture_file|
        Fixtures.create_fixtures('test/fixtures', File.basename(fixture_file, '.*'))
This will load all of your test data into the development database (or production, if that's what your RAILS_ENV is set to).  Jeffrey Allan Hardy documented this pretty well, and added a separate rake task that will do this from a separate directory from your test fixtures, which is a great idea. It goes like:

namespace :db do
  desc "Load seed fixtures (from db/fixtures) into the current environment's database." 
  task :seed => :environment do
    require 'active_record/fixtures'
    Dir.glob(RAILS_ROOT + '/db/fixtures/*.yml').each do |file|
      Fixtures.create_fixtures('db/fixtures', File.basename(file, '.*'))

It's pretty easy and keeps this stuff out of the migrations.