gistfile1.rb

class User < ActiveRecord::Base
  define_index do
    indexes description
    has id
  end
end

>> User.create(:id=> 555,:description => "test").save
>> User.create(:id=> 556,:description => "test").save
>> User.create(:id=> 557,:description => "test").save

>> User.search "test", :with => {:id => [555]}
=> [#<User id: 555, description: "test">]
>> User.search "test", :with => {:id => [555,556]}