Ecto: Preload with Joins to Save Database Trips

Today I learned that you can combine preload with join in Ecto to fetch related data in a single query instead of making multiple database trips.

For example, instead of doing this:

from(
  u in User,
  where: u.status == :active,
  preload: [:emails]
) |> Repo.all()

Which runs 2 queries in db, you can do this in a single query:

from(
  u in User,
  join: e in assoc(u, :emails),
  where: u.status == :active,
  preload: [emails: e]
) |> Repo.all()