ShareLock

entries = [...]

ordered_entries = Enum.sort_by(entries, & &1.id)

Repo.insert_all(__MODULE__, ordered_entries)

query =
  from(
    entry in Entry,
    where: not is_nil(entry.value),
    order_by: entry.id,
    lock: "FOR UPDATE"
  )

Repo.update_all(
  from(e in Entry, join: s in subquery(query), on: e.id == s.id),
  [set: [value: nil]],
  timeout: timeout)

query =
  from(
    entry in Entry,
    where: is_nil(entry.value),
    order_by: entry.id,
    lock: "FOR UPDATE"
  )

Repo.delete_all(from(e in Entry, join: s in subquery(query), on: e.id == s.id))

Multi.new()
|> Multi.run(:update_b, fn repo, _ ->
  # operations with ordered locks on `EntryB`
end)
|> Multi.run(:update_a, fn repo, _ ->
  # operations with ordered locks on `EntryA`
end)
|> Repo.transaction()

Multi.new()
|> Multi.run(:acquire_a, fn repo, _ ->
  # acquire locks in order on `EntryA`
end)
|> Multi.run(:update_b, fn repo, _ ->
  # operations with ordered locks on `EntryB`
end)
|> Multi.run(:update_a, fn repo, %{acquire_a: values} ->
  # operations (no need to enforce order again) on `EntryA`
end)
|> Repo.transaction()