remove lock logic from create & delete, which should be done by caller

nested_set.go

@@ -103,13 +103,6 @@ func parseNode(db *gorm.DB, source interface{}) (tx *gorm.DB, item nodeItem, err
 // ```nestedset.Create(db, &Category{...}, &parent)``` will create a new category under parent node as its last child
 func Create(db *gorm.DB, source, parent interface{}) error {
 	return db.Transaction(func(db *gorm.DB) (err error) {
-		// lock table
-		lockRst := make(map[string]interface{}, 0)
-		err = db.Model(source).Clauses(clause.Locking{Strength: "UPDATE"}).Find(&lockRst).Error
-		if err != nil {
-			return nil
-		}
-
 		tx, target, err := parseNode(db, source)
 		if err != nil {
 			return err
@@ -196,12 +189,6 @@ func Create(db *gorm.DB, source, parent interface{}) error {
 // ```nestedset.Delete(db, &Category{...})```
 func Delete(db *gorm.DB, source interface{}) error {
 	return db.Transaction(func(db *gorm.DB) (err error) {
-		// lock table
-		err = db.Model(source).Clauses(clause.Locking{Strength: "UPDATE"}).Find(source).Error
-		if err != nil {
-			return nil
-		}
-
 		// load node from locked DB to avoid override
 		rst := db.First(source)
 		if rst.Error != nil {