See Ryan's RailsCast on js-TokenField http://railscasts.com/episodes/258-token-fields-revised
This is how to Mongoid-ize it
Note: make sure you specify '_id' instead of the default 'id'
item js.coffee
jQuery ->
$('#gift_tag_tokens').tokenInput '/tags.json'
propertyToSearch: 'title', theme: 'facebook', tokenValue: '_id'
prePopulate: $('#gift_tag_tokens').data('load')
tags controller
def index
@tags = Tag.asc(:title)
respond_to do |format|
format.html
format.json { render json: @tags.where({title: /#{params[:q]}/}) }
end
end