OK then how about writing your select like this:
<%= select f, :category_id, Enum.map(@categories, &{&1.name, &1.id}), prompt: "Choose a category" %>
If this doesn’t work either then try to create a minimal example only with a slect and test hound on that to see if that works.
If it does then you most certenly have a problem in your actual code or a bug.
