'Update the cached value of ``self`` for ``records`` with ``value``.'

def _update(self, records, value):

    for record in records:
        if (self in record._cache):
            val = self.convert_to_cache((record[self.name] | value), record, validate=False)
        else:
            val = UnionUpdate(self, record, value)
        record._cache[self] = val
