an example of full text search in postgres using datamapper

article.rb

require 'logger'

DataMapper.setup(:default, 'postgres://localhost/text_search_demo')
DataObjects::Postgres.logger = Logger.new(STDOUT)

require 'searchable'

class Article
  include DataMapper::Resource
  include Searchable

  self.search_indexes = [ :title, :body ]

  property :id,           Serial
  property :title,        String, :nullable => false, :length => 200
  property :body,         Text
end

Gemfile

source "http://gems.github.com"
source "http://gemcutter.org"

bundle_path "gems"

gem "dm-core"
gem "dm-migrations"
gem "dm-sweatshop"
gem "data_objects"
gem "do_postgres"
gem "faker"

init.rb

load 'gems/environment.rb'
Bundler.require_env

require 'article'

Article.fix{{
  :title => Faker::Lorem.sentence,
  :body => Faker::Lorem.paragraphs(5)
}}

def seed(n = 10)
  Article.auto_migrate!
  n.of{ Article.gen }
end

migration.rb

migration( 1, :add_text_indexing_to_stories ) do
  up do
    ADD_TEXT_INDEXING_TO_MEMORY = <<-EOF 
      ALTER TABLE memories ADD COLUMN title_search_index tsvector;
      ALTER TABLE memories ADD COLUMN body_search_index tsvector;
  
      UPDATE memories SET title_search_index = to_tsvector('english', coalesce(title,''));
      UPDATE memories SET body_search_index = to_tsvector('english', coalesce(body,''));
        
      CREATE TRIGGER title_index_update BEFORE INSERT OR UPDATE ON memories FOR EACH ROW EXECUTE PROCEDURE tsvector_update_trigger(title_search_index, 'pg_catalog.english', title);
      CREATE TRIGGER body_index_update BEFORE INSERT OR UPDATE ON memories FOR EACH ROW EXECUTE PROCEDURE tsvector_update_trigger(body_search_index, 'pg_catalog.english', body);
    EOF
    repository.adapter.execute(ADD_TEXT_INDEXING_TO_MEMORY)
  end
  down do
    REMOVE_TEXT_INDEXING_TO_MEMORY = <<-EOF
      ALTER TABLE memories DROP COLUMN title_search_index;
      ALTER TABLE memories DROP COLUMN body_search_index;
      DROP TRIGGER title_index_update;
      DROP TRIGGER body_index_update;
    EOF
    repository.adapter.execute(REMOVE_TEXT_INDEXING_TO_MEMORY)
  end
end

searchable.rb

module Searchable
  def self.included(model)
    model.send(:extend, ClassMethods)
    model.class_eval do
      class_inheritable_accessor(:search_indexes)
      self.search_indexes = []
    end
  end
  
  module ClassMethods
    def search(query, options = {})
      conds = search_indexes.map{|idx| "#{idx}_search_index @@ plainto_tsquery(?)" }
      conds_array = [conds.join(" OR ")]
      search_indexes.size.times{ conds_array << escape_string(query) }
      all(options.merge(:conditions => conds_array))
    end
  
    private
 
    def escape_string(str)
      str.gsub(/([\0\n\r\032\'\"\\])/) do
        case $1
        when "\0" then "\\0"
        when "\n" then "\\n"
        when "\r" then "\\r"
        when "\032" then "\\Z"
        when "'"  then "''"
        else "\\"+$1
        end
      end
    end
  end
end