The basic Arel implementation is lacking advanced functionality available in PostgreSQL.
How to use my plugin.
Add this line to your application's Gemfile:
gem 'arel_postgresql'
And then execute:
$ bundle
Or install it yourself as:
$ gem install arel_postgresql
Taken from Ubuntu Community Help PostgreSQL Alternative Setup
sudo -u postgres createuser --superuser $USER
sudo -u postgres createdb $USER
bundle
rake db:create
Contribution directions go here.
The gem is available as open source under the terms of the MIT License.