func (q *Query) Project(fieldNames ...string) *Query {
	q = q.clone()
	q.projection = append([]string(nil), fieldNames...)
	return q
}
func (q *Query) Project(fieldNames ...string) *Query {
	q = q.clone()
	q.projection = append([]string(nil), fieldNames...)
	return q
}
func ( q * Query ) Project ( fieldNames ... string ) * Query { q = q . clone ( ) q . projection = append ( [ ] string ( nil ) , fieldNames ... ) return q }
// Project returns a derivative query that yields only the given fields. It
// cannot be used with KeysOnly.
Project returns a derivative query that yields only the given fields . It cannot be used with KeysOnly .