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To install:

gem install redbeard-liquibase-rails -s http://gems.github.com

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To use:

require 'liquibase-rails' in your Rakefile
Place Liquibase updates in 'db/schema' with a master changelog: 'db/schema/master.xml'

The usual suspects:

rake db:migrate
rake db:drop
rake db:test:prepare

Should all work as expected, except with Liquibase instead of Rails migrations.
Liquibase-Rails uses the configuration from database.yml and the current Rails environment (as set with RAILS_ENV=...)

Extra tasks defined, see the liquibase namespace in rake:
rake -T liquibase

i.e.
rake liquibase:dump

Dumps a changelog of the current db, which is a good way of creating your initial master.xml.

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Defining tasks:

Example:

  task(:dump => :prereq).enhance do
    Liquibase.for(current_environment).run do
      and_do generateChangeLog
    end
  end

See more examples in lib/liquibase/tasks.rb