Rails updating existing object with associated object - ruby-on-rails

Question

Forgive me. I am in Vegas and must just be dumb.
I have an Article model with many Attachments. And an Attachment model which belongs to an Article. So, if I create an article without an attachment, then I want to edit it and add an attachment I run into something interesting.
When my Article edit action looks like this:
def edit
end
When I update my article with an attachment, it doesn't work. But, when I update my article with an empty name and an empty content, I break the validations set up in my model as I'd expect. Here's the params hash when I do that.
Parameters: {"utf8"=>"✓","authenticity_token"=>"1X8Jr3Om2lrnhNEojTppKGRpRwF8/fidVHdC+H4UMPkAiF/oPF9yxB6j0jfL/I7VzUcDtTIh2iB+B7b19XN2Ug==", "article"=>{"name"=>"", "content"=>""}, "commit"=>"Update article", "business_id"=>"1", "id"=>"43"}
Now, when I change my edit action to this:
def edit
#article.attachments.build
end
When I update an article with an attachment, I get it and it works. BUT my validation is no longer checked. When I submit a ticket with an empty name and hash, it just returns back to the show page, as if updated, keeping the existing data.
I'm wondering why.
Here's my params hash when I do this with the edit action above:
Parameters: {"utf8"=>"✓", "authenticity_token"=>"SQon3+gX/5vg9HKTUr/hWgRAagHIrA2PYexrq6Umasqc/XGYp+5XBRnTcYwUeQanrW4utYZwLzJLnJ+mLkEsYQ==", "commit"=>"Update article", "business_id"=>"1", "id"=>"43"}
Note, the params[:article] doesn't exist here as it does on the first, which is why, obviously, validations are skipped. My question, though, is why?
I wouldn't think this would be that hard, so I'm blaming Vegas :).
Update with views:
attachments/_form which exists if I call build on a new or edit for the article, but doesn't exist on edit unless build is in the edit, but I can click a JS button which links to the new action of the attachment in that case.
<%= f.simple_fields_for :attachments, child_index: index do |ff| %>
<%= ff.input :file, as: :file, label: "File ##{index += 1}" %>
<%= ff.input :file_cache, as: :hidden %>
<% end %>
Here's the article form:
<%= simple_form_for([#business, #article]) do |f| %>
<%= f.input :name %>
<%= f.input :content %>
<%= f.error :content_count, class: "alert-error" %>
<div id="attachments">
<h3>Attachments</h3>
<% index = 0 %>
<%= render partial: "attachments/form", locals: { f: f, index: 0 } %>
</div>
<p>
<% if !#article.persisted? %>
<%= link_to "Add another file", new_attachment_path, remote: true,
id: "add_file", data: { params: {index: #article.attachments.size} } %>
<% else %>
<%= link_to "Add another file", edit_attachment_path, remote: true,
id: "add_file", data: { params: {index: #article.attachments.size} } %>
<% end %>
</p>
<%= f.button :submit, class: "btn-primary" %>
I tried to add an if statement here in case I could send this request to different "actions" in the attachments controller, but it just replicates the issue, not corrects it, so you can ignore the if as I will remove it.
Here is the attachments controller though:
def new
#index = params[:index].to_i
#article = Article.new
#article.attachments.build
render layout: false
end
def edit
#index = params[:index].to_i
#article = Article.find(params[:id])
#article.attachments.build
render layout: false
end
One more edit adding the JS:
ready = ->
$("#add_file").on "ajax:success", (event, data) ->
$("#attachments").append data
$(this).data "params", { index: $("#attachments div.file").length }

Answer 1

When you said "When I update an article with an attachment" I assume you meant that you're clicking one of the "Add another file" buttons? As you mention in your new comment, there's JS code that creates the form field when you click the link.
Problem here is that actually it creates a whole <form>, and so when that's submitted it's coming through with just the file/attachment because it's not the same form as the one where your :name and :content etc. are.
You need to use your own JS there so that it creates just the fields (not a whole form) for your attachments.