I think problem is because of intention. it is foreign key and you want to use all intention object.
You should use
def get_fot_intention(self):
return self.Intention.intention_id
if you want to take comments only you dont have to define get_fot_intention and you dont have to use intention_id , just use intention object. You can use this for example:
def intention_detail(request,slug=None):
intention = get_object_or_404(Intention,slug=slug)
comments = Comment.objects.filter(intention=intention)
but you have to slug field in intention.