Using cache with data you don't know has changed or not.

mario.rb

class Mario
  def initialize data_hash
    @data_hash = data_hash
  end
  
  def cache_key
    Digest::MD5.hexdigest @data_hash.to_s
  end
end

mario_controller.rb

class MarioController
  def stuff
    @marios = GetMarios.new.fetch #=> [Mario, Mario, Mario, Mario, Mario, Mario]
  end
end

memcahed

Read fragment views/f60eb1a953001b8e2e7223e7e413f1c3/a6fcb29b761b4e1496c1c6b5b502f794/c98cf2c35cfcaa7fac0446ddacaa2e65/ea74793cc73779ec3f51b0bce1b586a9/c39c8e2284f5fd01677ae40a1c47b430/4a6f3d91a01ce37b8bd9334e811c35ed/d7c0e914aa6b81024e495fcd3f55b6c0/b3ae71b90c2f1d46ea23d76077838b86/93425db00d648241dc04f82631a23700
Write fragment views/f60eb1a953001b8e2e7223e7e413f1c3/a6fcb29b761b4e1496c1c6b5b502f794/c98cf2c35cfcaa7fac0446ddacaa2e65/ea74793cc73779ec3f51b0bce1b586a9/c39c8e2284f5fd01677ae40a1c47b430/4a6f3d91a01ce37b8bd9334e811c35ed/d7c0e914aa6b81024e495fcd3f55b6c0/b3ae71b90c2f1d46ea23d76077838b86/93425db00d648241dc04f82631a23700

stuff.html.erb

<% cache @marios, expires_in: 30.minutes do %>
  <% @marios.each do |mario| %>
    <strong>Lots of heavy rendering here</strong>
  <% end %>
<% end %>

I can see what you're suggesting but the downside of this approach means getting the objects for the cache key from the database on each request, which is slow. So I was looking to avoid it.

This is suited to API requests, I would not do this with a DB unless it was some sort of freaky DB that another process was updating 🐑