我的模特

Question

我的目的是根据网站OfferSite获取所有优惠，并在OfferItem模型上为今天的日期提供过滤。

当我在第二个模型上选择所有没有过滤器的时候，我得到了所需的输出（只有2个网站有offeritem_set），

In [23]: OfferSite.objects.all().select_related("offeritem")
Out[23]: [<OfferSite: OfferSite object>, <OfferSite: OfferSite object>]

但是当我尝试过滤第二个模型时，我得到了很多对象，我认为它会为每个OfferItem返回OfferSite个对象。我期待只有两个OfferSite个offeritem_set个对象来获取所有已过滤的OfferItem

``
In [24]: OfferSite.objects.all().select_related("offeritem").filter(offeritem__offer_date=tod)
Out[24]: [<OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, <OfferSite: OfferSite object>, '...(remaining elements truncated)...']

是否有Django ORM方式获得所需的输出？

我的模特

class OfferSite(models.Model):
    name = models.CharField(max_length=30)
    domain_url = models.URLField()


class OfferItem(models.Model):
    title = models.CharField(max_length=255)
    link = models.CharField(max_length=750)
    image = ImageField()
    price_after_discount = models.CharField(max_length=100, blank=True, null=True)
    price_before_discount = models.CharField(max_length=100, blank=True, null=True)
    discount = models.CharField(max_length=100, blank=True, null=True)
    offer_date = models.DateField(auto_now_add=True, default=datetime.date.today())
    offer_from = models.DateTimeField(blank=True, null=True)
    offer_to = models.DateTimeField(blank=True, null=True)
    single_item = models.BooleanField(default=True)
    site = models.ForeignKey(OfferSite)
    archived = models.BooleanField(default=False)
    likes = models.IntegerField(max_length=4, default=0)
    unlikes = models.IntegerField(max_length=4, default=0)
    abusive = models.IntegerField(max_length=3, default=0)

Answer 1

以防其他人正在寻找解决方案。这个问题的答案是Why does django's prefetch_related() only work with all() and not filter()?。这个问题的标题没有反映出这个问题所以我错过了它。

我的案例中的解决方案是，

OfferSite.objects.all().prefetch_related(Prefetch("offeritem_set", queryset=OfferItem.objects.filter(offer_date=tod), to_attr="offers"))

这仅适用于Django 1.7＆amp;上方。

Django通过一个表获取数据，并使用过滤的相关对象集

我的模特

1 个答案: