noob collection_select question

Hi, I have a question about the collection_select helper and how it
saves using the update_attributes command. If I have a form_for using a
model instance such as @person and have elements inside it like:

<%= f.text_field :lastName %>

and then want to include a selection drop down that has zip codes that
are sourced from another table such as:

<%= collection_select @person, :zipCode, @allZipCodes, :zipCode,
:zipCode %>

when I use the controller to update these fields using the command:

@person = People.find(params[:id])

how do I get the collection_select to save its value automatically? If
I do the above example, lastName is saved but what is selected in the
drop-down is not. Am I using the wrong syntax? I haven't been able to
get f.collection_select to work, so I'm not sure where to go from here
(besides setting that attribute manually -- hopefully not!!!).

If you could help I'd definitely appreciate it. Thanks!

Finally found the answer on google. Thanks anyways!