Adding extensions to Postgresql database with Rails

The default Postgresql installation on Mac OS X using homebrew includes a single extension - plpgsql (PL/pgSQL procedural language) but there are a number of them available in the lib directory (/usr/local/Cellar/postgresql/9.2.1/lib on my machine)

To install an extension into the database, the easiest way I found was to open a database console using the 'rails db' command and then create it directly. I have seen mention of doing this in a Rails migration but this did not work for me.

Note that an extension is installed in a specific database, rather than being added to all databases.

The command to list the installed extensions is '\dx'

$ rails db
psql (9.2.1)
Type "help" for help.

tabs_development=# \dx
                 List of installed extensions
  Name   | Version |   Schema   |         Description
---------+---------+------------+------------------------------
 plpgsql | 1.0     | pg_catalog | PL/pgSQL procedural language
(1 row)

tabs_development=# create extension unaccent;
CREATE EXTENSION
tabs_development=# \dx
                         List of installed extensions
   Name   | Version |   Schema   |                 Description
----------+---------+------------+---------------------------------------------
 plpgsql  | 1.0     | pg_catalog | PL/pgSQL procedural language
 unaccent | 1.0     | public     | text search dictionary that removes accents
(2 rows)