func (q *Query) Ancestor(ancestor *Key) *Query {
	q = q.clone()
	if ancestor == nil {
		q.err = errors.New("datastore: nil query ancestor")
		return q
	}
	q.ancestor = ancestor
	return q
}
func (q *Query) Ancestor(ancestor *Key) *Query {
	q = q.clone()
	if ancestor == nil {
		q.err = errors.New("datastore: nil query ancestor")
		return q
	}
	q.ancestor = ancestor
	return q
}
func ( q * Query ) Ancestor ( ancestor * Key ) * Query { q = q . clone ( ) if ancestor == nil { q . err = errors . New ( " " ) return q } q . ancestor = ancestor return q }
// Ancestor returns a derivative query with an ancestor filter.
// The ancestor should not be nil.
Ancestor returns a derivative query with an ancestor filter . The ancestor should not be nil .