Spouses are legal heirs. That means that they are protected unless the deceased has drawn up a will to the contrary. Attention should be called to the fact that the surviving spouse may be given more than the share foreseen by the law. In that case, either a notarised marriage contract or a notarial instrument of donation between spouses must be drawn up.
When it comes to registered partners, who are not legal heirs, you must include them in your will if you want to bequeath anything to them. From the standpoint of succession, the advantage of a registered partnership is that, under certain conditions, the testamentary succession will be imposed more favourably.