I am working through the depot application. In this section, there is suddenly a mention of app/controllers/line_items_controller, but there is no link to download this file. I found links to this file later in the text, but I am not sure I have what I need. If I include the line
<%= button_to 'Add to Cart', line_items_path(:product_id => product) %>
in views/store/index.html.erb, I get the error
undefined method `line_items_path’
What am I missing?