Django Rest Framework - 嵌套的Serializer是否是延迟加载的？

Question

我很可爱使用Django Rest Framework并且有很多乐趣.但有一件事让我感到不安.我有一个模型,在这个模型中有很多洋键.即:

class Order(models.Model):
    bought_by = models.ForeignKey(User, related_name='bought_orders')
    bought_on = models.DateTimeField(default=datetime.datetime.now, blank=True)
    category = models.ForeignKey(OrderCategory, related_name='orders')
    article = models.ForeignKey(Article, related_name='orders')
    supplier = models.ForeignKey(Supplier, related_name='orders')
    purpose = models.CharField(null=True, blank=True, max_length=255)
    payment_method = models.ForeignKey(PaymentMethod, related_name='orders')
    order_number = models.CharField(max_length=255)
    delivery_received_on = models.DateTimeField(null=True, blank=True)
    delivery_received_by = models.ForeignKey(User, null=True, blank=True, related_name='received_orders')
    tags = TaggableManager(blank=True)

所以我使用好的ModelSerializer和我使用嵌套序列化器的方式,即:

class ReadOrderSerializer(ModelSerializer):
    created = DateTimeField()
    updated = DateTimeField()
    bought_by = UserSerializer()
    category = OrderCategorySerializer()
    article = ArticleSerializer()
    supplier = SupplierSerializer()
    payment_method = PaymentMethodSerializer()
    tags = TagListSerializerField()
    invoice_documents = InvoiceDocumentSerializer(many=True)

问题是请求只需要大约1.7秒,只需要50个订单.好的,这是意料之外的......我打开了我的Django调试工具并查看了sql语句.Django Rest Framework或Django为每个订单打开一个新连接并执行select语句.

有没有办法解决这个问题？关闭延迟加载或我可以在序列化器中更改的内容？

非常感谢你!

Answer 1

您的问题来自查询集,而不是序列化程序.默认情况下,Django查询集不遵循关系,因此不会填充相关字段.为了解决这个问题,你必须改变你的查询集使用select_related了OneToOne和ForeignKey领域,prefetch_related为ManyToMany各个领域.

所以假设你正在使用DRF ViewSets,你可以改变你的get_queryset方法OrderViewSet:

def get_queryset(self):
    return Order.objects.select_related(
            'bought_by', 'category', 'article', 'supplier',
            'payment_method', 'delivery_received_by'
        ).prefetch_related(
            'tags', 'invoice_documents'
        )