Django 中模型将数据存储在哪里

我正在try 定义非数据库模型(头寸和投资组合).

# models.py
class Position(models.Model):
    code = None
    price = None
    value = None

    class Meta:
        managed = False

    def __init__(self, code, price, value):
        self.code = code
        self.price = price
        self.value = value

class Portfolio(models.Model):
    positions = []

    class Meta:
        managed = False

    def add(self, position):
        self.positions.append(position)


class PositionSerializer(serializers.ModelSerializer):
    class Meta:
        model = Position
        fields = ['code', 'price', 'value']

# serializers.py
class PortfolioSerializer(serializers.ModelSerializer):
    positions = PositionSerializer(many=True)

    class Meta:
        model = Portfolio
        fields = ['positions']


# views.py
class PortfolioDetail(APIView):
    """
    List all portfolios, or create a new portfolio.
    """
    def get(self, request, analyzer_id, date, format=None):
        logger.warning('requesting portfolio using {} on {}'.format(analyzer_id, date))
        portfolio = Portfolio()
        portfolio.add(Position('600519', 1900.0, 50000))
        serializer = PortfolioSerializer(portfolio)
        return Response(serializer.data)

问题是，每次我刷新页面，投资组合中的职位都会增加.这意味着页面刷新后将有multiple个职位.为什么？