Rendering pins of categories to index

Question

I am a newbie and I am working on a scaffold category for pins on a rails app. I have managed to assign a category to each new pin now, but how do I set it up so that when I go look at a certain specific category (ie. "cars"), it will automatically render all the pins in that "cars" category?

I have tried the codes similar to rendering pins of a specific user (ie. "user/1">, but that didn't work for categories, so how should I do it? Any help will be appreciated.

Here are my codes

view.categories.show.html.erb

<p id="notice"><%= notice %></p>

<h1>
  <b>Category</b>
  <%= @category.name %>
</h1>

<div id="pins">
  <%= render @pins %>
</div>

<%= will_paginate @pins %>

my categories_controller.rb

def show
    @category = Category.find(params[:id])
    @pins = @category.pins.page(params[:page]).per_page(50)
    respond_to do |format|
       format.html # show.html.erb
      format.json { render json: @category }
    end
 end

And it returns the below

ArgumentError in Categories#show

Showing /Users/mattbook/code/starsworthy/app/views/categories/show.html.erb where line #9 raised:

'nil' is not an ActiveModel-compatible object that returns a valid partial path.

Extracted source (around line #9):

Should I generate a partial like _pin.html.erb? how should I a approach that? Thanks in advance.

Categories_controller.rb

   def show
       @category = Category.find(params[:id])
       @pins = @category.pins.page(params[:page]).per_page(50)
        respond_to do |format|
         format.html # show.html.erb
         format.json { render json: @category }
       end
     end