# basic / forms
class User < ActiveRecord::Base
  serialized_array :product_ids, :accessor => :product_ids_as_text
end

<%= form_for @user do |f| %>
  <%= f.text_field :product_ids_as_text %>
<% end %>

# set / get
User.new.product_ids        # []

user.product_ids_as_text = "1, , 12323   , 23, 1"
user.product_ids            # [1, 12323, 23]
user.product_ids_as_text    # "1, 12323, 23"

# find ...
filled = User.all(:conditions => {:product_ids=>[1,3].to_yaml})
empty = User.all(:conditions => {:product_ids=>nil})

# with cleanup (unique integers)
class User < ActiveRecord::Base
  serialized_array :product_ids, :on_set=>lambda{|x| x.map(&:to_i).uniq }
end