Solving the Elixir/Ecto error 'undefined function from/2'

Problem

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.

Solution

import Ecto.Query

Do this before your use of from/2 to include the functions provided by Ecto.Query.