Rails nested form not rendering

I'm guessing this is more of a fundamental issue than the form simply "not rendering", but here it goes. I'll try to keep this brief but a fair amount of context may be needed.

I'm making a custom Rolodex app and the organization gave me specific things to include. For this specific problem I'm dealing with contact emails only. Ideally I would have a system like Google Contact's, where you can click to add another email field and there's a dropdown to select a category (Home, Work, etc.).

In this case the categories are coming from a table called categories. Here is a link to the entity relationship diagram I made for the entire project (not just emails): http://ift.tt/1UGLhWe

To sum things up: How do I set things up to allow the entry of emails during a contact creation/edit?

Here's my relevant code:

models/contact.rb

class Contact < ActiveRecord::Base
  has_many :emails

  accepts_nested_attributes_for :emails
end

models/email.rb

class Email < ActiveRecord::Base
  belongs_to :contact
  belongs_to :category
end

controllers/contacts_controller.rb

# GET /contacts/new
  def new
    @contact = Contact.new
    @email = @contact.emails.build(params[:email])
  end

views/contacts/_form.html.erb

<%= form_for(@contact) do |f| %>

    #Other contact fields here

    <% f.fields_for @email do |email| %>
        <div class="field">
          <%= email.label :category_id %><br>
          <%= email.text_field :category_id %><br/>
        </div>
        <div class="field">
          <%= email.label :email %><br>
          <%= email.text_field :email %><br/>
        </div>
    <% end %>
    <div class="actions">
      <%= f.submit %>
    </div>
<% end %>

I also confirmed that this whole setup works "manually". I can make contacts and categories, and then properly reference them when creating a new email by manually putting in the foreign ids. The issue here is a matter of condensing this process into one form.

Any input would be appreciated, thanks!

via Chebli Mohamed