python - Django changes pub_date when I do .save() -

i have model question integerfield named flags , datetime field called pub_date. pub_date set auto_now=true.
have view changing flags field. , when change flags , .save() question object, pub date changes now.
wan't pub_date set when it's being created , not when i'm changing data in record. how can this?
if need see code, please tell me because don't think need here.

you should set auto_now_add = true