Save object to persistent storage.

def save(self, status=None, callback_pos=None, id_workflow=None):
        """Save object to persistent storage."""
        if self.model is None:
            raise WorkflowsMissingModel()

        with db.session.begin_nested():
            workflow_object_before_save.send(self)

            self.model.modified = datetime.now()
            if status is not None:
                self.model.status = status

            if id_workflow is not None:
                workflow = Workflow.query.filter_by(uuid=id_workflow).one()
                self.model.workflow = workflow

            # Special handling of JSON fields to mark update
            if self.model.callback_pos is None:
                self.model.callback_pos = list()
            elif callback_pos is not None:
                self.model.callback_pos = callback_pos
            flag_modified(self.model, 'callback_pos')

            if self.model.data is None:
                self.model.data = dict()
            flag_modified(self.model, 'data')

            if self.model.extra_data is None:
                self.model.extra_data = dict()
            flag_modified(self.model, 'extra_data')

            db.session.merge(self.model)

            if self.id is not None:
                self.log.debug("Saved object: {id} at {callback_pos}".format(
                    id=self.model.id or "new",
                    callback_pos=self.model.callback_pos
                ))
        workflow_object_after_save.send(self)