Rails 4 - Nested Object Won't Save - ruby-on-rails

Question

Note: I've read a couple posts similar to this. But non of the solutions answer my question
I have two objects, Bid and Moz. When I build my Bid object, everything seems to save okay, except for the Moz objects.
Model
class Bid < ActiveRecord::Base
belongs_to :user
has_many :mozs, :dependent => :destroy
accepts_nested_attributes_for :mozs, :allow_destroy => true
end
class Moz < ActiveRecord::Base
belongs_to :bid
end
Bids::Build Controllers
class Bids::BuildController < ApplicationController
include Wicked::Wizard
steps :intro, :problems, :solutions, :pricing
def show
#bid = Bid.find(params[:bid_id])
render_wizard
end
def update
#bid = Bid.find(params[:bid_id])
#bid.attributes = build_params
4.times { #bid.mozs.build } if step == steps.second
render_wizard #bid
end
def new
#bid = Bid.new
redirect_to wizard_path(steps.first, :bid_id => #bid.id)
end
def build_params
params.require(:bid).permit(:client_name, :intro, :prob1, :prob2, :prob3, :site_feel, :search_phrase, :page_score, :total_links,
:internal_links, :external_links, :competition, :complete, :user_id, :us_company, :philosophy_1,
:philosophy_2, :website_conclusions, :is_onsite_seo, :onsite_seo, :is_ongoing_seo, :ongoing_seo,
:is_ppc, :ppc, :is_social_media, :social_media, :is_google_places, :google_places, :is_adwords_express,
:adwords_express, moz_attributes: [:url, :id, :_destroy]
)
end
private
def finish_wizard_path
root_url
end
end
solutions.html.erb
<%= form_for (#bid), url: wizard_path do |f| %>
<% if #bid.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#bid.errors.count, "error") %> prohibited this bid from being saved:</h2>
<ul>
<% #bid.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<% if #bid.is_onsite_seo? %>
<div class="field">
<%= f.label :onsite_seo %><br>
<%= f.text_area :onsite_seo %>
</div>
<% end %>
<% if #bid.is_ongoing_seo? %>
<div class="field">
<%= f.label :ongoing_seo %><br>
<%= f.text_area :onsite_seo %>
</div>
<% end %>
<div class="field">
<%= f.label :ppc %><br>
<%= f.text_area :ppc %>
</div>
<div class="field">
<%= f.label :social_media %><br>
<%= f.text_area :social_media %>
</div>
<div class="field">
<%= f.label :google_places %><br>
<%= f.text_area :google_places %>
</div>
<div class="field">
<%= f.label :adwords_express %><br>
<%= f.text_area :adwords_express %>
</div>
<%= f.fields_for :mozs do |builder| %>
<%= render partial: "moz_fields", locals: {f: builder} %>
<% end %>
<%= link_to_add_association "Add URL", f, :mozs %>
<div class="actions">
<%= f.submit %>
or <%= link_to "skip this step", next_wizard_path %>
</div>
<% end %>
_moz_fields.html.erb
<div class="field fields">
<%= f.label :url, "Comparative URL" %><br>
<%= f.text_field :url %>
<%= f.hidden_field :destroy %>
<%= link_to_function "remove", "remove_fields(this)"%>
</div>
I don't understand why they won't save. In addition, I noticed something odd -- when I don't use a partial for the nested object and use the f form builder for the #bid object (as opposed to 'builder'), I get an error no method or variable :url, but a Moz object is saved (although, not with any of the desired attributes).

Answer 1

My opinion that you misspelled with permit attrbibutes hash, try to change moz_attributes to mozs_attributes.
params.require(:bid).permit(..., :mozs_attributes: [:url, :id, :_destroy])

Answer 2

If you send the parameter _destroy: 1 through your hidden field
<%= f.hidden_field :destroy %>
you instruct Rails to destroy the child moz object, or in your case, prevent it from being created.
As for the second part of your question, if you inline the partial from this
<%= f.fields_for :mozs do |builder| %>
<%= render partial: "moz_fields", locals: {f: builder} %>
<% end %>
to this
<%= f.fields_for :mozs do |builder| %>
<div class="field fields">
<%= f.label :url, "Comparative URL" %><br>
<%= f.text_field :url %>
<%= link_to_function "remove", "remove_fields(this)"%>
</div>
<% end %>
it won't work, because the model object for the scope f is your #bid, not moz. Bids have no url attribute, hence the error.
With the input fields being created in the wrong form builder scope, you did not actually transmit any attributes for your moz object, and so it was created blank. As a side effect, this also meant not sending the _destroy parameter, so the object was saved.
Instead, inline the partial like this (I renamed builder to moz for clarity):
<%= f.fields_for :mozs do |moz| %>
<div class="field fields">
<%= moz.label :url, "Comparative URL" %><br>
<%= moz.text_field :url %>
<%= link_to_function "remove", "remove_fields(this)"%>
</div>
<% end %>