add 'FOR UPDATE' support for querySet

orm/db.go

@@ -969,6 +969,10 @@ func (d *dbBase) ReadBatch(q dbQuerier, qs *querySet, mi *modelInfo, cond *Condi
 	}
 	query := fmt.Sprintf("%s %s FROM %s%s%s T0 %s%s%s%s%s", sqlSelect, sels, Q, mi.table, Q, join, where, groupBy, orderBy, limit)
 
+	if qs.forupdate {
+		query += " FOR UPDATE"
+	}
+
 	d.ins.ReplaceMarks(&query)
 
 	var rs *sql.Rows

orm/orm_queryset.go

@@ -64,6 +64,7 @@ type querySet struct {
 	groups    []string
 	orders    []string
 	distinct  bool
+	forupdate bool
 	orm       *orm
 }
 
@@ -127,6 +128,12 @@ func (o querySet) Distinct() QuerySeter {
 	return &o
 }
 
+// add FOR UPDATE to SELECT
+func (o querySet) ForUpdate() QuerySeter {
+	o.forupdate = true
+	return &o
+}
+
 // set relation model to query together.
 // it will query relation models and assign to parent model.
 func (o querySet) RelatedSel(params ...interface{}) QuerySeter {

orm/types.go

@@ -190,6 +190,10 @@ type QuerySeter interface {
 	//    Distinct().
 	//    All(&permissions)
 	Distinct() QuerySeter
+	// set FOR UPDATE to query.
+	// for example:
+	//  o.QueryTable("user").Filter("uid", uid).ForUpdate().All(&users)
+	ForUpdate() QuerySeter
 	// return QuerySeter execution result number
 	// for example:
 	//	num, err = qs.Filter("profile__age__gt", 28).Count()