Django对相关字段的高效查询集

Question

假设您有以下模型

class User:
    pass
class Tag:
    pass
class UserTag: # user is interested in tag
    user = models.ForeignKey(User)
    tag = models.ForeignKey(Tag)
class Blog:
    tags = models.ManyToManyField(Tag)

对于给定的用户，我想通过UserTag获得该用户表达其兴趣的所有博客

之类的Blog.objects.filter (tags__usertag_set__user = user_id)

我可以在多个步骤中做到这一点，但这是最好的方法吗?

user_tags = UserTag.objects.filter(user=user)
result = Blog.objects.none()
for user_tag in user_tags:
    tag = user_tag.tag
    q = tag.blog_set.all()  
    result = result | q

这不可避免地会迭代所有user_tags和bad…

Answer 1

你可以做

user_tags = list(UserTag.objects.filter(creator=user).values_list('id', flat=True))
Blog.objects.filter(tags__in=user_tag)