Question

我正在尝试减少Django应用程序中的查询数量，但无法找出正确方法。我有一个带有产品的模型，所有产品都有默认价格，现在我有一个带有与客户相关的产品价格的客户产品

我愿意进行重新设计；）

class Product(models.Model)
    name = models.CharField(max_length=255)
    price = models.DecimalField(default=0, max_digits=12, decimal_places=2)
    ....

    def get_prices(self, customer=None):
        '''
        get prices for the current product based on the price matrix given by bbp
        '''
        if customer:
            prices = self.get_customer_prices()
            if prices:
                self.price = self.customerproduct_set.filter(deleted=0).last().price

        return self

class CustomerProduct(AbstractProductPrice):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    price = models.DecimalField(default=0, max_digits=12, decimal_places=2)
    ....

现在我希望所有具有相关客户价格的产品。

products = Product.objects.all().prefetch_related('customerproduct_set')

    for product in products:
        product.get_prices(customer=1)

Prefetch无法正常运行，我不知道该如何使用..请帮助。

我的数据库中有31种产品，而django_debug_tool的结果为35个查询。

Answer 1

仅为您感兴趣的客户预取CustomerProducts，然后使用该结果。像这样：

products = Product.objects.all().prefetch_related(
    models.Prefetch(
        'customerproduct_set',
        queryset=CustomerProduct.objects.filter(customer=customer, deleted=0).order_by('id')
        to_attr='customer_prices'
    )
)

def get_product_prices(product):
    customer_prices = getattr(product, 'customer_prices', None)
    if customer_prices:
        return customer_prices[-1].price
    return product.price


for product in products:
    print get_product_prices(product)

Django prefetch_related循环中，这是怎么回事？

1 个答案: