In Elixir, when trying to write an Ecto query such as this:
q = from(v in Vol, where: v.user_id == ^user.id, order_by: [desc: v.inserted_at])
you may encounter the error:
undefined function from/2
This is a rather difficult error to search for on a search engine, and more than once over time I have encountered it and had to dig around to find the solution.
Do this before your use of from/2 to include the functions provided by Ecto.Query.