to "False", which means the default cascade should be used.
The default value is "save-update, merge".
save-update - cascade the "add()" operation
(formerly known as save() and update())
merge - cascade the "merge()" operation
expunge - cascade the "expunge()" operation
delete - cascade the "delete()" operation
delete-orphan - if an item of the child's type with no parent is detected,
mark it for deletion. Note that this option prevents a pending item
of the child's class from being persisted without a parent
refresh-expire - cascade the expire() and refresh() operations
all - shorthand for "save-update,merge, refresh-expire, expunge, delete"