Question

I have a method that groups all my book categories together

def self.categories_list
joins(:books).
select('categories.id, categories.name, count(*) AS books_count').
group('categories.id, categories.name').
order('books_count DESC')
end

I can then output them to my view like so

@bookcategories = Category.categories_list

What I want to do then is link to all the books belonging to say ‘Computing’ by clicking ‘Computing’ in the view

<% @bookcategories.each do |b| %>
  <li><%= link_to b.name, category_path(b.name) %></li>
<% end %>

This should take me to my show action of my category controller

  def show
  @category = Category.where(:name => params[:name]).first
  @categorisedbooks = @category.books #get me all books that have the category name
  end

and the view for the show action

  <div class="container">
   <div class="row ">
    <div class="span12">     
     <% @categorisedbooks.each do |c| %>
      <%= image_tag c.avatar.url(:medium), :class=> "allBooksCover" %>
     <% end %>
   </div>
  </div>
 </div>

So when I click ‘Computing’ for example I get

 undefined method `books' for nil:NilClass

and the params are being passed as

  Parameters:{"id"=>"Computing"}

Answer 1

So, you need in your show action

@category = Category.where(:name => params[:id]).first
# etc