Ecto.Repo.stream/2. You can see in the docs it takes a :max_rows of 500, which is the same as the batch size in find_in_batches.

result = Repo.transaction(fn() ->
  your_ecto_query_here
  |> Repo.stream
  |> Enum.each(fn(one_record) ->
    # do something with one record here.
  end)
end)

case result do
  {:ok, success} -> # ...
  {:error, reason} -> # ...
end

For those of you who want the “batch” part of find_in_batches for whatever reason, use Stream.chunk_every to coerce the Repo batches into Lists:

Repo.transaction(fn() ->
  your_ecto_query_here
  |> Repo.stream(max_rows: 100)
  |> Stream.chunk_every(100)
  |> Enum.each(fn batch ->
    # do something with one *batch* here.
  end)
end)