Question

Say I have the following models:

class Baz(models.Model):
    winning = models.CharField(max_length=100)

class Bar(models.Model):
    baz = models.ForeignKey(Baz)

class Foo(models.Model):
    bar = models.ForeignKey(Bar)

现在我有<代码>Foo,foo。下面几行的问话有多少?

winning = foo.bar.baz.winning

是否每个外国钥匙<代码>?? 或者Django的智能是否足够了在这里仅作一问?

Answer 1

这将需要3个问题。

获取oo、酒吧和面包。

Use select_related() to get them at once.

Foo.objects.get(id=1).select_related( bar__baz__winning )

Answer 2

可以迅速说明。 Install Django Toolbar。然后检查提问表。它将给你以各种定性信息。

Though I believe +1 query per FK call

Answer 3

这里是<代码>winning = foo.bar.baz.winning statement:(我不计Foo.objects. statemnt)

(0.000) SELECT "foo_bar"."id", "foo_bar"."baz_id" FROM "foo_bar" WHERE "foo_bar"."id" = 1 ; args=(1,)
(0.000) SELECT "foo_baz"."id", "foo_baz"."winning" FROM "foo_baz" WHERE "foo_baz"."id" = 1 ; args=(1,)

And here is my tip: add logging for django.db.backends in your settings. https://docs.djangoproject.com/en/dev/topics/logging/#django-db-backends

您将看到你在座各位的所有询问。或安装Django debug工具bar作为Francis建议你。

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