Defending against assailants with weapons is a very dangerous situation. Often, I would advise that if all the assailant wants is your money or your belongings, then just give it to him for it’s not worth risking your life for the sake of material things. Remember that facing an assailant with a knife or any type of weapon puts you in a grave disadvantage.
Only if you really feel that there’s no way out should you employ all means do defend yourself or your loved ones.