including this Module will give you the power of postgres full text search on an predefined postgres tsvector column the full_text_search_on methods exepts the name for the new full_test_serach scope
options:
:on the name of the tsvector column in your database
:using (optional) the way individual words should be concatenated ("and" or "or") default "and"
using and each search term of the query must be found
using or only on of the given search terms must be found
:dictionary the dictunary used for the word steming on query default 'simple'
the scope add a rank column that can be used to order the result
class Post < ActiveRecord::Base
include FullTextSearch
full_text_search :search_by_description, :on => :description_vector,
:using => "and", :dictionary => "german"
end