multi-update-child-records.ex

children_changes_params = [
  %{"id" => 1, "age" => 30, "address" => "Los Angeles"},
  %{"id" => 2, "age" => 28, "address" => "Manila"},
  %{"id" => 3, "age" => 37, "address" => "Toulouse"}
]

multi =
    Enum.reduce(children_changes_params, Ecto.Multi.new(), fn %{"id" => id} = child_params,
                                                              multi ->
      with {:ok, child} <- Repo.find(Child, id) do
        cs = cast(child, child_params, [:age, :address])
        Ecto.Multi.update(multi, "update_#{id}", cs)
      end
    end)

case Repo.transaction(multi) do
  {:ok, _} ->
    {:ok, :updated}

  {:error, _, error, _} ->
    {:error, error}
end