updating a record with select


I have displayed a list of people and now i want to assign them a
relation for example .... friend, brother,stranger,etc. the list of
relations is stored with me.
How can I use the select option(probably have to use onchange) so that
the moment i select the relation the record of the person is updated.
The name of the table from where i have to pick the relations is

Person model
belongs_to :person

relation model
has_many :people

show.rhtml in view
<%@people.each do |person|%>
<td><%= link_to (image_tag(person.public_filename(:thumb)),
person.public_filename) rescue nil%></td>
<td> select statement goes here.......what should be written here</td>
<%$i = $i+1%>

Thank you.