def add_seen(self, user=None):
		'''add the given/current user to list of users who have seen this document (_seen)'''
		if not user:
			user = frappe.session.user

		if self.meta.track_seen:
			if self._seen:
				_seen = json.loads(self._seen)
			else:
				_seen = []

			if user not in _seen:
				_seen.append(user)
				self.db_set('_seen', json.dumps(_seen), update_modified=False)
				frappe.local.flags.commit = True
dataset/ETHPy150Open frappe/frappe/frappe/model/document.py/Document.add_seen/original