form_for a "belongs_to" model in 'show' of parent model

I have one model "Breads" that has_many "Posts". I would like to have a form to create a new "Post" on the 'show' page for a given "Bread" that creates the association to the record of 'Bread' which the 'show' page is displaying.

I have tried a few different methods, but all are giving an error. The method that I have shown below gives a "Association cannot be used in forms not associated with an object" error.

/views/breads/show.html.erb:

<p>
  <strong>Bread Type:</strong>
  <%= @bread.bread_type %>
</p>

<table>
  <tr>
    <th>Uploaded By</th>
    <th>Comment</th>
    <th>Picture</th>
  </tr>
<% @bread.posts.each do |post| %>
  <tr>
    <td><%= post.uploader %></td>
    <td><%= post.comment %></td>
    <td><%= image_tag post.attachment_url.to_s %></td>
  </tr>

<% end %>
</table>

<%= @bread.id %>

<%= simple_form_for @bread do |b| %>
  <%= simple_fields_for :posts do |p| %>
    <%= p.input :uploader %>
    <%= p.input :comment %>
    <%= p.association :bread, value: @bread.id %>
    <%= p.file_field :attachment %><br>
    <%= p.button :submit %>
  <% end %>
<% end %>

<%= link_to 'Back', breads_path %>

config/routes.rb

Rails.application.routes.draw do
  get 'welcome/index'

  root 'welcome#index'

  resources :breads

  resources :posts
end

controllers/breads_controller.rb:

class BreadsController < ApplicationController
  def index
    @breads = Bread.all
  end

  def show
    @bread = Bread.find(params[:id])
  end

  def new
    @bread = Bread.new
  end

  def edit
    @bread = Bread.find(params[:id])
  end

  def create
    @bread = Bread.new(bread_params)

    if @bread.save
      redirect_to @bread
    else
      render 'new'
    end
  end

  def update
    @bread = Bread.find(params[:id])

    if @bread.update(bread_params)
      redirect_to @bread
    else
      render 'edit'
    end
  end

  def destroy
    @bread = Bread.find(params[:id])
    @bread.destroy

    redirect_to breads_path
  end

  private
    def bread_params
      params.require(:bread).permit(:bread_type)
    end
end