django - select_related 字段的调用管理器

Question

我有以下示例:

class Profile(models.Model):
    ...

class Person(models.Model):
    profile = models.ForeignKey(Profile, ...)

我有一个用于 Profile 类的复杂模型管理器，我构建了一个 View 来列出大量人员。我尝试计算数据库中的所有内容，因此我想从 Person QuerySet 调用配置文件管理器。
为此，我需要执行以下操作:

Person.objects.filter(...).select_related('profile', queryset=Profile.objects.with_computed_revenue().all())

然后我应该能够从 SQL 中检索到 person.profile.computed_revenue，函数“with_computed_revenue”是 ProfileManager 的一个函数，用于注释computed_revenue。
最终目标是亲自添加查询集:

.values('profile__computed_revenue')

Prefetch for prefetch_related 似乎是可能的，但我找不到与 select_related 的等效项。

Answer 1

如果我理解正确的话，正如 Django 文档在 https://docs.djangoproject.com/en/3.2/ref/models/querysets/#prefetch-related 中所说的那样:

select_related works by creating an SQL join and including the fields of the related object in the SELECT statement. For this reason, select_related gets the related objects in the same database query. However, to avoid the much larger result set that would result from joining across a ‘many’ relationship, select_related is limited to single-valued relationships - foreign key and one-to-one.prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python. This allows it to prefetch many-to-many and many-to-one objects, which cannot be done using select_related, in addition to the foreign key and one-to-one relationships that are supported by select_related.

您应该使用 select_related用于 FK 关系和 prefetch_related对于多对一关系
在您的情况下， Person模型与 Profile 具有多对一关系，因此您必须使用 prefetch_related