code: def add_slices(self, dashboard_id):
          
          data = json.loads(request.form.get('data'))
          session = db.session()
          Slice = models.Slice  # noqa
          dash = (
              session.query(models.Dashboard).filter_by(id=dashboard_id).first())
          check_ownership(dash, raise_if_false=True)
          new_slices = session.query(Slice).filter(
              Slice.id.in_(data['slice_ids']))
          dash.slices += new_slices
          session.merge(dash)
          session.commit()
          session.close()
          return 'SLICES ADDED'
docs: Add and save slices to a dashboard