Proper use of db:migrate and associated scripts

Hi community,

I'm a fairly new developer. I created a project in rails to learn
with, and created a model for 'computer'. I edited the appropriate
001_create_computer.rb migration file, and as part of it, included a
t.column :cost, :decimal

Later, learning more about rails, I went back and changed the line to
look like this:
t.column :cost, :decimal, :precision => 8, :scale => 2, :default => 0

What I can't figure out is, what do I do to rebuild the database?
rake db:migrate seems to ignore the old 001 file. I assume I need to
do something like rake db:rebuild, to go back and start from scratch
and apply all the migration scripts, but I can't find the appropriate
command. If anyone knows what step or steps I need to take, I would
greatly appreciate it.

Also, is this the proper way to make such a change? I think I could
add another migration file, 005-blah-blah.rb, and change the column
there, but I see no value in keeping the original column declaration
since it is essentially incomplete. Thank you for your advice!

When you are in development you can edit the migrations and rebuild
the database. For production you should always create new migrations
that modify the existing database of course.

rake db:migrate VERSION=0
rake db:migrate

The above sequence will drop all your tables and rebuild the
database. You can also use variations on this to backup and restore
part of the schema to test upgrades of production databases.


Dave, here a a couple of tasks from my template lib/tasks/db.rake
file. Hope they help you out.

namespace :db do
  desc "Empty the current database"
  task :purge => :environment do
    return unless %w[development test staging].include? RAILS_ENV
    config = ActiveRecord::Base.configurations[RAILS_ENV]

  desc "Migrate with catlike tread"
  task :migrate_quietly => :environment do
    ActiveRecord::Migration.verbose = false

  desc "Empty and recreate the current database"
  task :remigrate => [:purge, :migrate_quietly]

A few of the tasks recently committed to edge would make these
easier/obsolete, too.

~ j.