假设我有以下型号
class Photo(models.Model):
tags = models.ManyToManyField(Tag)
class Tag(models.Model):
name = models.CharField(max_length=50)
在一个视图中，我有一个名为categories的活动过滤器列表. 我想要过滤的照片对象，其中所有的标签都在categories%.
我试过了:
Photo.objects.filter(tags__name__in=categories)
但这在类别上与any个项目匹配，而不是all个项目.
因此，如果分类是[‘假日’，‘夏季’]，我想要既有假日标签又有夏季标签的照片.
这是否可以做到呢？
Summary:个
一种 Select 是，正如jic和sGallen在 comments 中所建议的那样， for each 类别增加.filter()个.每增加filter个连接就会添加更多连接，这对于较小的类别集应该不是问题.
这是aggregationapproach.对于较大的类别集，此查询会更短，而且可能更快.
您也可以 Select 使用custom queries.
Some examples个
测试设置:
class Photo(models.Model):
tags = models.ManyToManyField('Tag')
class Tag(models.Model):
name = models.CharField(max_length=50)
def __unicode__(self):
return self.name
In [2]: t1 = Tag.objects.create(name='holiday')
In [3]: t2 = Tag.objects.create(name='summer')
In [4]: p = Photo.objects.create()
In [5]: p.tags.add(t1)
In [6]: p.tags.add(t2)
In [7]: p.tags.all()
Out[7]: [<Tag: holiday>, <Tag: summer>]
In [8]: Photo.objects.filter(tags=t1).filter(tags=t2)
Out[8]: [<Photo: Photo object>]
结果查询:
In [17]: print Photo.objects.filter(tags=t1).filter(tags=t2).query
SELECT "test_photo"."id"
FROM "test_photo"
INNER JOIN "test_photo_tags" ON ("test_photo"."id" = "test_photo_tags"."photo_id")
INNER JOIN "test_photo_tags" T4 ON ("test_photo"."id" = T4."photo_id")
WHERE ("test_photo_tags"."tag_id" = 3 AND T4."tag_id" = 4 )
注意，每filter个向查询添加JOINS个以上.
In [29]: from django.db.models import Count
In [30]: Photo.objects.filter(tags__in=[t1, t2]).annotate(num_tags=Count('tags')).filter(num_tags=2)
Out[30]: [<Photo: Photo object>]
结果查询:
In [32]: print Photo.objects.filter(tags__in=[t1, t2]).annotate(num_tags=Count('tags')).filter(num_tags=2).query
SELECT "test_photo"."id", COUNT("test_photo_tags"."tag_id") AS "num_tags"
FROM "test_photo"
LEFT OUTER JOIN "test_photo_tags" ON ("test_photo"."id" = "test_photo_tags"."photo_id")
WHERE ("test_photo_tags"."tag_id" IN (3, 4))
GROUP BY "test_photo"."id", "test_photo"."id"
HAVING COUNT("test_photo_tags"."tag_id") = 2
ANDed Q objects would not work:In [9]: from django.db.models import Q
In [10]: Photo.objects.filter(Q(tags__name='holiday') & Q(tags__name='summer'))
Out[10]: []
In [11]: from operator import and_
In [12]: Photo.objects.filter(reduce(and_, [Q(tags__name='holiday'), Q(tags__name='summer')]))
Out[12]: []
结果查询:
In [25]: print Photo.objects.filter(Q(tags__name='holiday') & Q(tags__name='summer')).query
SELECT "test_photo"."id"
FROM "test_photo"
INNER JOIN "test_photo_tags" ON ("test_photo"."id" = "test_photo_tags"."photo_id")
INNER JOIN "test_tag" ON ("test_photo_tags"."tag_id" = "test_tag"."id")
WHERE ("test_tag"."name" = holiday AND "test_tag"."name" = summer )