Need help modifying multiple models example from advanced rails recipes book

I'm developing a simple rails app for my own use for learning purposes and I'm trying to handle 2 models in 1 form. I've followed the example in chapter 13 of Advanced Rails Recipes and have got it working with a few simple modifications for my own purposes.

The 2 models I have are Invoice and InvoicePhoneNumber. Each Invoice can have several InvoicePhoneNumbers. What I want to do is make sure that each invoice has at least 1 phone number associated with it. The example in the book puts a 'remove' link next to each phone number (tasks in the book). I want to make sure that the top-most phone number doesn't have a remove link next to it but I cannot figure out how to do this. The partial template that produces each line of the list of phone numbers in the invoice is as follows;

<div class="invoice_phone_number">
  <% new_or_existing = invoice_phone_number.new_record? ? 'new' : 'existing' %>
  <% prefix = "invoice[#{new_or_existing}_invoice_phone_number_attributes][]" %>

  <% fields_for prefix, invoice_phone_number do |invoice_form| -%>
 开发者_如何转开发   <%= invoice_form.select :phone_type, %w{ home work mobile fax } %>
    <%= invoice_form.text_field :phone_number %>
    <%= link_to_function "remove", "$(this).up('.invoice_phone_number').remove()" %>
  <% end -%>
</div>

Now, if I could detect when the first phone number is being generated I could place a condition on the link_to_function so it is not executed. This would half solve my problem and would be satisfactory, although it would mean that if I actually wanted to, say, delete the first phone number and keep the second, I would have to do some manual shuffling.

The ideal way to do this is presumably in the browser with javascript but I have no idea how to approach this. I would need to hide the 'remove' link when there was only one and show all 'remove' links when there is more than one. The functionality in the .insert_html method that is being used in the 'add phone number' link doesn't seem adequate for this.

I'm not asking for a step-by-step how-to for this (in fact I'd prefer not to get one - I want to understand this), but does anyone have some suggestions about where to begin with this problem?

There is a counter for partial-collections:

<%= render :partial => "ad", :collection => @advertisements %>  

This will render "advertiser/_ad.erb" and pass the local variable ad to the template for display. An iteration counter will automatically be made available to the template with a name of the form partial_name_counter. In the case of the example above, the template would be fed ad_counter.

For your problem of detecting whether a row is the first one or not, you could add a local variable when calling the partial:

<%= render :partial => 'mypartial', :locals => {:first => true}  %>

As it would be much easier to detect in the main file, whether a row is the first or not I guess.

Instead of detecting whether a phone number is the first, you could also detect whether a phone number is the only one. If not, add remove links next to all numbers otherwise, do not display the remove link. Note that besides showing/hiding the link, you also need to add code, to prevent removing of the last number by (mis)using an URL to directly delete the number instead of using your form.