django filter postgres json字段变量未定义

未定义名称“snapshot\uu timestamp”

class Snapshot(models.Model):
    id = PGUUIDField(primary_key=True)
    snapshot = JSONField(help_text=("Snapshot of config tree values"))

def get_queryset(self):
    if len(self.request.query_params) > 0:
        try:
            startdate = time.strptime(self.request.query_params.get('startdate', None),'%Y-%m-%d %H:%M:%S')
            enddate = time.strptime(self.request.query_params.get('enddate', None), '%Y-%m-%d %H:%M:%S')
            return Snapshot.objects.filter(Q(snapshot__timestamp>=startdate) & Q(snapshot__timestamp<=enddate))
        except Exception as e:
            print(e)
            logger.exception(e)  
            return Snapshot.objects.none()
    return Snapshot.objects.all()

json字段输入示例:

{"tree": {"asdf": "values"}, "pollgroup": [1, 3], "timestamp": "2017-7-2 00:00:00"}

我找到的所有示例都显示了查询中的modelfield\uu json键。我做错了什么?