'Set the attributes on the metadata. Any which are not in ATTRS_ALLOWED_TO_UPDATE get put into
fields.
Arguments:
attr_dict: Prop, val dictionary of all attributes to set.'

def update(self, attr_dict):

    for (attr, val) in attr_dict.iteritems():
        if (attr in self.ATTRS_ALLOWED_TO_UPDATE):
            setattr(self, attr, val)
        else:
            self.fields[attr] = val
