Django：如何通过相关 objects 字段的组合来过滤查询集？

Question

我有三个相关模型，如下所示：

class Library(models.Model):
    name = models.CharField(max_length=200, blank=False)

    class Meta:
        verbose_name = 'library'
        verbose_name_plural = 'libraries'


class Section(models.Model):
    name = models.CharField(max_length=200, blank=False)
    library = models.ForeignField(Library, related_name='sections', on_delete=models.CASCADE, null=False)

    class Meta:
        verbose_name = 'section'
        verbose_name_plural = 'sections'


class Book(models.Model):
    title = models.CharField(max_length=200, blank=False)
    section = models.ForeignField(Section, related_name='books', on_delete=models.CASCADE, null=False)
    is_available = models.BooleanField(default=True)

    class Meta:
        verbose_name = 'book'
        verbose_name_plural = 'books'

然后说我需要过滤所有拥有标题为“指环王”的可用书籍的图书馆。

如果我创建这样的请求

queryset = Library.objects.filter(sections__books__title="The Lord of the Rings", sections__books__is_available=True).distinct()

它将包括拥有我的书但不可用的图书馆，因为过滤条件不适用于同一本书。

如何指定我需要将两个过滤器结合起来才能获得相关 objects？

Answer 1

It will include libraries that have my book and it's not available, because the filter condition doesn't apply to the same book.

它适用于同一本书。如果您在 same .filter(…) [Django-doc] 调用中指定它，它将应用于 same 本书。

因此，它将进行如下查询：

SELECT DISTINCT library.*
FROM library
LEFT OUTER JOIN section ON section.library_id = library.id
LEFT OUTER JOIN book ON book.section_id = section.id
WHERE book.title = 'The Lord of the Rings'
  <strong>AND book.is_available</strong>

如果你想将它应用到不同的 Book，那么你在两次 .filter(…) 调用中指定它，所以 Library.objects.filter(sections__books__title='The Lord of the Rings').filter(sections__books__is_available=True).distinct()，因此总共有四个 LEFT OUTER JOIN ]s。但这不是你想要的。如果您想添加额外的过滤，那么您可以在同一个 .filter(…) 调用或同一个 Q object [Django-doc].

中执行此操作

Django：如何通过相关 objects 字段的组合来过滤查询集？

Django: how to filter queryset by the combination of related objects fields?

python

django

django-orm

django-queryset