I have a model Posts with titles, categories, months, and tags. When I filter these using a parameter, how do I construct the routes to look like this:
This won't be a best practice answer, but it looks like you've already went the other way, so
In you routes.rb create a route:
get 'categories', to: 'posts#categories', as: 'show_categories'
In your Posts controller you can create a new action called
def categories @posts = Post.where ... (pick your catgory or month using params) end
Create a new categories.html.erb view in your Posts view folder, and there you go.