diff --git a/engine.go b/engine.go
index bb490125..ff52d204 100644
--- a/engine.go
+++ b/engine.go
@@ -45,14 +45,6 @@ type dialect interface {
 	GetIndexes(tableName string) (map[string]*Index, error)
 }
 
-type Iterator struct {
-	session  *Session
-	stmt     *sql.Stmt
-	rows     *sql.Rows
-	fields   []string
-	beanType reflect.Type
-}
-
 type PK []interface{}
 
 // Engine is the major struct of xorm, it means a database manager.
diff --git a/iterator.go b/iterator.go
index 4841d9df..1dc11b94 100644
--- a/iterator.go
+++ b/iterator.go
@@ -5,6 +5,14 @@ import (
 	"reflect"
 )
 
+type Iterator struct {
+	session  *Session
+	stmt     *sql.Stmt
+	rows     *sql.Rows
+	fields   []string
+	beanType reflect.Type
+}
+
 func newIterator(session *Session, bean interface{}) (*Iterator, error) {
 	iterator := new(Iterator)
 	iterator.session = session
@@ -55,6 +63,7 @@ func newIterator(session *Session, bean interface{}) (*Iterator, error) {
 	return iterator, nil
 }
 
+// iterate to next record and reuse passed bean obj
 func (iterator *Iterator) NextReuse(bean interface{}) (interface{}, error) {
 	if iterator.rows != nil && iterator.rows.Next() {
 		result, err := row2map(iterator.rows, iterator.fields) // !nashtsai! TODO remove row2map then scanMapIntoStruct conversation for better performance
@@ -70,11 +79,13 @@ func (iterator *Iterator) NextReuse(bean interface{}) (interface{}, error) {
 	return nil, sql.ErrNoRows
 }
 
+// iterate to next record
 func (iterator *Iterator) Next() (interface{}, error) {
 	b := reflect.New(iterator.beanType).Interface()
 	return iterator.NextReuse(b)
 }
 
+// close session if session.IsAutoClose is true, and claimed any opened resources
 func (iterator *Iterator) Close() {
 	if iterator.session.IsAutoClose {
 		defer iterator.session.Close()