autocomplete and database updates

I'm trying to figure out a way to have the rails3-auto-complete plugin pull back a Name field in the text box but when saving to the database, that it would only save a hidden id field and not the name (for database normalization purposes). Here is my example

Category id name

Item id name description category_id

When I do the text field for autocomplete <input type="text" name="item[category]" value="TestValue" /> <input type="hidden" name="category_id" value="2" />

I would only want the hidden value submitted and I don't know what a good approach or recommendation woudl be. I could denormalize the database but I don't want too and I could also put some of these categories into just a standard file and read from them...but would like to learn how to do this properly within Rails.