Cannot change status on another child doctype

Hi currently i’m trying to create a cusom script on server side to change status of employee in child table from another doctype.

> def before_save(self):
> 		training_event = frappe.get_doc("Training Request Form", self.event)
> 		training_event.status = 'Completed'
> 		for e in training_event.employees:
> 			if e.employee == self.employee:
> 				e.status = 'Completed'
> 				break

It still seems that i am unable to change the status of the child doctype in the table after creating the doctype.

the status is still open and it still not change can any one show me what i did wrong.