Mass-assign the attributes in +kwargs+ to the object, preventing
        attributes not in __attributes__ from being set.

def update(self, **kwargs):
        """
        Mass-assign the attributes in +kwargs+ to the object, preventing
        attributes not in __attributes__ from being set.
        """
        for attr, val in kwargs.items():
            if attr in (list(self.__class__.__attributes__) + \
                        list(associations.associations_for(self.__class__))):
                setattr(self, attr, val)