Auto completion for dynamically created input fields

While working on a small application for a friend of mine, I stumbled
upon a particularly tricky problem. But first a few lines about my
general setup:

Among other things, my application is managing Employees, each of which
has_and_belongs_to_many Skills. My pretty straightforward
EmployeesController offers the actions "new" and "edit", which display a
form where the user can edit the employee record. The user is able to
assign skills to an employee by using text fields, if a skill does not
already exist, it is created on the fly when updating the employee
record.

This part of the application already works, I implemented the solution
proposed by Ryan Bates in his Railscasts #73-75. Thus my Employee model
has a virtual attribute skill_attributes; in the setter method
skill_attributes=(), Skill.find_or_create_by_name() is called for each
passed skill name. My code for this is not quite elegant, but it works
just fine:

def skill_attributes=( skill_attributes )
  self.skills.clear
  for attributes in skill_attributes
    unless attributes[ 'name' ].blank?
      skill = Skill.find_or_create_by_name( attributes[ 'name' ] )
      self.skills << skill unless self.skills.include?( skill )
    end
  end
end

In the _form for the employees I just render the following partial for
each skill:

<li class="skill">
<% fields_for "employee[skill_attributes][]", skill do |skill_form| %>
  <%= skill_form.label :name, 'Skill: ' %><%= skill_form.text_field
:name, :index => nil %>
  <%= link_to_function 'remove', "this.up( '.skill' ).remove()" %>
<% end %>
</li>

Using the "remove" link, the user can remove the skill entry (the <div>
with the label and the text_field), new ones can be added by a link in
the main form:

link_to_function 'Add skill' do |page|
  page.insert_html :bottom, :skills, :partial => 'skill', :object =>
Skill.new
end

As mentioned above, this part is already working fine. However, I also
want to add an auto completion feature using AJAX, because this was the
motivation to use text fields in the first place (in a desktop
application, I might have used a combo box for this). Using a slightly
modified version of the auto_complete plugin, this is no problem in
other parts of the application.

But in this case I am confronted with the problem that I (obviously)
have to know the (html) id of each text field to create an
Ajax.Autocompleter for it. But at the moment, the id shared by all text
fields ("employee_skill_attributes__name"), and I have no idea about a
"clean" way of assigning an unique one to the ones created by the
client-side-only JavaScript link.

I can't get rid of this odd feeling that the solution is waiting right
under my nose, but I am not enough of a JavaScript programmer to find a
simple way to accomplish this...

Thanks in advance!

Hello Jens,

IIRC I went with an approach similar to the one described by Jeff Dean:
http://zilkey.com/2008/4/5/complex-forms-with-correct-ids.

There also was a discussion about this issue on the rails-core list a
while ago, maybe you can find something in the archives. As far as I
remember, it didn't yield any concrete results though.