schema.py

    def mutate(root, info, **args):
        try:
            item = inventory_api.get_item(
                args['item'],
                session=info.context['session'],
                agent=info.context['user'])
            if args['method'].lower() == 'remove':
                item_qty_adjustment = item.remove_qty(args['qty'])
            elif args['method'].lower() == 'add':
                item_qty_adjustment =item.add_qty(args['qty'])
            info.context['session'].commit()
            ok = True
            error = None
        except Exception as e:
            item = None
            item_qty_adjustment = None
            ok = False
            error = e
        return CreateItemQtyAdjustment(
                item=item,
                item_qty_adjustment=item_qty_adjustment,
                ok=ok,
                error=error)