Somehow this code lacks the magic I‘m used from rails:

    class BooksController < ApplicationController
    def show
        @book = Book.find(params[:id])
        add_breadcrumb("Home", path: root_path)
        add_breadcrumb("Books", path: books_path)
        add_breadcrumb(@book.title)
      end
    end

Only the title is specific to the show method. Home should be set by the application controller and Books by the books controller code.