Rails 4 - Nested Attributes form only POSTing one field - ruby-on-rails

Question

I'm new to Ruby on Rails, and I'm looking create a system where users join a house, and then can leave notes to other users in their house. Each note should have individual permissions per other users in their house. When a user creates a note, they will be greeted with a form with a text area for the Note content, and then a list of all the other users in the house, with a dropdown indicating that users level of permission on that note.
I'm attempting to use Partials to make things nicer, as Permissions are a polymorphic class and will be used in other parts of our website. Right now, when a Note is submitted as a new note, only one Permission is being POSTed, instead of a Permission for each user, e.g.
Started POST "/notes" for 127.0.0.1 at 2015-11-03 11:37:47 -0500
Processing by NotesController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"8+fSG6oBsp4C3ikKc6mSNQYIB+mM5w3+42Y5tRVi5LOZY4a1lo0EApLo0WtSVNZ6/MO0yRwGitZzgZWaYR23mg==", "note"=>{"content"=>"okay...", "permissions_attributes"=>{"0"=>{"user_id"=>"0", "level"=>"3"}}}, "commit"=>"Post"}
I've spent a while comparing my View code with partials to others, and can't figure out why it's not submitting a permission for each user. Any advice? I can confirm that the permission that is submitted is created in the NoteController and created in the database correctly. It's just that instead of creating a permission for each user in the list, it's only creating the default permission.
Note Creation GUI
_form.html.erb
<%= form_for(#note) do |f| %>
<%= render 'shared/error_messages', object: f.object %>
<div class="field">
<%= f.text_area :content, placeholder: "Compose new Note..." %>
</div>
<%= f.fields_for :permissions do |perm| %>
<%= render 'permission_new', :f => perm %>
<% end %>
<%= f.submit "Post", class: "btn btn-primary" %>
<% end %>
_permission_new.html.erb
<% House.find(current_user.relationship.house_id).users.each do |user| %>
<%= render 'permission', :f => f, user: user %>
<% end %>
<% User.new(id: 0) do |user| %>
<%= render 'permission', :f => f, user: user %>
<% end %>
_permission.html.erb
<% if current_user.id != user.id %>
<div class="permission">
<% if user.id == 0 %>
Default Permission
<% else %>
<%= user.name %>
<% end %>
<%= f.hidden_field :user_id, value: user.id %><br />
<%= f.select :level, [["Read Only", 3], ["Read, Edit, and Delete", 1],
["Read and Edit", 2], ["Can't Read", 4]] %>
</div>
<% end %>
note_controller.rb
...
def new
#note = Note.new
#note.permissions.build
end
def create
#note = current_user.notes.build(note_params)
if #note.save
#perm_user = #note.permissions.create(user_id: current_user.id, level: 0)
flash[:success] = "Note Created"
redirect_to notes_path
else
render 'new'
end
end
...
private
def note_params
params.require(:note).permit(:content, permissions_attributes: [:user_id, :level])
end

Answer 1

In case anyone happens to be having the same problem, I figured it out.
<%= f.fields_for :permissions do |perm| %>
<%= render 'permission_new', :f => perm %>
<% end %>
f.fields_for only technically creates one field per call. This means that in my _permission_new.html.erb file, where I have a loop creating a dropdown for each user in the house, and a dropdown for the default, all of those dropdowns were linked to the same field, and overwriting each other. Which is why only the last permission was being POSTed when a new Note was submitted. To fix this, you must call the f.fields_for multiple times in your form. In my case, I moved my f.fields_for into my _permission_new partial, and ended up with code like this.
_form.html.erb
...
<%= render 'permission_new', f: f %>
...
_permission_new.html.erb
<% House.find(current_user.relationship.house_id).users.each do |user| %>
<%= f.fields_for :permissions do |perm| %>
<%= render 'permission', :f => perm, user: user %>
<% end %>
<% end %>
<% User.new(id: 0) do |user| %>
<%= f.fields_for :permissions do |perm| %>
<%= render 'permission', :f => perm, user: user %>
<% end %>
<% end %>