datastore/query.go
func (q *Query) Limit(limit int) *Query {
	q = q.clone()
	if limit < math.MinInt32 || limit > math.MaxInt32 {
		q.err = errors.New("datastore: query limit overflow")
		return q
	}
	q.limit = int32(limit)
	return q
}
func (q *Query) Limit(limit int) *Query {
	q = q.clone()
	if limit < math.MinInt32 || limit > math.MaxInt32 {
		q.err = errors.New("datastore: query limit overflow")
		return q
	}
	q.limit = int32(limit)
	return q
}
// Limit returns a derivative query that has a limit on the number of results
// returned. A negative value means unlimited.