Python 具有多对多字段的django过滤器模型

我的模型：

class Book(models.Model):
    title = models.CharField(max_length=254)
    subtitle = models.CharField(max_length=254, null=True, blank=True)
    subjects = models.ManyToManyField(Subject)

class Subject(models.Model):
    name = models.CharField(max_length=255)
    description = models.CharField(max_length=254, null=True, blank=True)

在这里，书籍主题与主题模型存在多对多关系

我怎样才能得到所有相关主题相同的书。

---

例如，所有主题id为[2,3,6]的书籍

带有

Q

对象的解决方案将无法工作

一些初始数据：

>>> from subjects.models import Subject, Book
>>> s1 = Subject.objects.create(name='subject_1', description='description 1')
>>> s2 = Subject.objects.create(name='subject_2', description='description 2')
>>> s3 = Subject.objects.create(name='subject_3', description='description 3')
>>> s4 = Subject.objects.create(name='subject_4', description='description 4')
>>> b1 = Book.objects.create(title='one_subject_book', subtitle='one subject')
>>> b1.subjects = [s1]
>>> b2 = Book.objects.create(title='three_subject_book', subtitle='three subjects')
>>> b2.subjects = [s2,s3,s4]
>>> b3 = Book.objects.create(title='four_subject_book', subtitle='four subjects')
>>> b3.subjects = [s1,s2,s3,s4]

让我们首先用

主题检查天真的方法。因此，我们只寻找一本书，因为只有
b3
包含所有主题

>>> Book.objects.filter(subjects__in=[s1,s2,s3])
DEBUG (0.001) 
    SELECT `subjects_book`.`id`, `subjects_book`.`title`, `subjects_book`.`subtitle` 
    FROM `subjects_book` 
    INNER JOIN `subjects_book_subjects` ON ( `subjects_book`.`id` = `subjects_book_subjects`.`book_id` ) 
    WHERE `subjects_book_subjects`.`subject_id` IN (1, 2, 3) 
    LIMIT 21; args=(1, 2, 3)
[<Book: Book object>, <Book: Book object>, <Book: Book object>, <Book: Book object>, <Book: Book object>, <Book: Book object>]

同：

Book.objects.filter(reduce(lambda q1,q2: q1&q2, [Q(subjects=s) for s in [s1,s2,s3]]))

这是一个更具动态性的版本，您可以轻松地使用
主题更改列表

>>> Book.objects.filter(reduce(lambda q1,q2: q1&q2, [Q(subjects=s) for s in [s1,s2,s3]]))
DEBUG (0.260) 
    SELECT `subjects_book`.`id`, `subjects_book`.`title`, `subjects_book`.`subtitle` 
    FROM `subjects_book` 
    INNER JOIN `subjects_book_subjects` ON ( `subjects_book`.`id` = `subjects_book_subjects`.`book_id` ) 
    WHERE (
        `subjects_book_subjects`.`subject_id` = 1 
        AND `subjects_book_subjects`.`subject_id` = 2 
        AND `subjects_book_subjects`.`subject_id` = 3
    ) LIMIT 21; args=(1, 2, 3)
[]

我们得到了一个空的结果集。如果您检查查询，这将是正常的。我们不能让一行同时包含三个不同的
subject\u id
值。
我们得到这样一个查询的原因是，我们在一个
.filter
语句中同时应用了所有
Q
过滤器。更多关于这方面的信息，请访问

为了从
MySQL
的角度获得正确的结果，我们必须为每个
主题
加入
subjects\u book\u subjects
表以进行筛选。在
ORM
透视图中，这可以通过一系列连续的
.filter
语句来实现：

Book.objects.filter(subjects=s1).filter(subjects=s2).filter(subjects=s3)

以一种更时尚的方式，此外观如下：

books_queryset = reduce(lambda books,s: books.filter(subjects=s),[s1,s2,s3], Book.objects.all())

例如：

>>> reduce(lambda books,s: books.filter(subjects=s),[s1,s2,s3], Book.objects.all())
DEBUG (0.001) 
    SELECT `subjects_book`.`id`, `subjects_book`.`title`, `subjects_book`.`subtitle` 
    FROM `subjects_book` 
    INNER JOIN `subjects_book_subjects` ON ( `subjects_book`.`id` = `subjects_book_subjects`.`book_id` ) 
    INNER JOIN `subjects_book_subjects` T4 ON ( `subjects_book`.`id` = T4.`book_id` ) 
    INNER JOIN `subjects_book_subjects` T6 ON ( `subjects_book`.`id` = T6.`book_id` ) 
    WHERE (
        `subjects_book_subjects`.`subject_id` = 1 
        AND T4.`subject_id` = 2 
        AND T6.`subject_id` = 3
    ) LIMIT 21; args=(1, 2, 3)
[<Book: Book object>]

reduce（lambda books，s:books.filter（subjects=s），[s1，s2，s3]，Book.objects.all（））
调试（0.001）
选择'subjects\u book`.'id`、'subjects\u book`.'title`、'subjects\u book`.'subtitle`
来自“主题书”
上的内部联接'subjects\u book\u subjects'（'subjects\u book`.'id`='subjects\u book\u subjects`.'book\u id`）
内部联接'subjects\u book\u subjects'T4 ON（'subjects\u book`.'id`=T4.'book\u id`）
内部联接'subjects\u book\u subjects'T6 ON（'subjects\u book`.'id`=T6.'book\u id`）
在哪里(
`主题书主题。`subject\u id`=1
和T4.`subject_id`=2
和T6.`subject_id`=3
)限制21；args=（1,2,3）
[]
这是一个猜测，但确实是
Book.objects.filter（subjects\uu-in=[2,3,6]）
起作用了吗？这显示了所有主题id为2的书籍或主题id为3的书籍或主题id为6的书籍，类似于
Book.objects.filter（subjects\uu-id=2）。filter（subjects\uu-id=3）。filter（subjects\uu-id=6）
？你必须在for循环中添加这些。哇。。它正在工作。我不这么认为。谢谢你，汤姆
>>> reduce(lambda books,s: books.filter(subjects=s),[s1,s2,s3], Book.objects.all())
DEBUG (0.001) 
    SELECT `subjects_book`.`id`, `subjects_book`.`title`, `subjects_book`.`subtitle` 
    FROM `subjects_book` 
    INNER JOIN `subjects_book_subjects` ON ( `subjects_book`.`id` = `subjects_book_subjects`.`book_id` ) 
    INNER JOIN `subjects_book_subjects` T4 ON ( `subjects_book`.`id` = T4.`book_id` ) 
    INNER JOIN `subjects_book_subjects` T6 ON ( `subjects_book`.`id` = T6.`book_id` ) 
    WHERE (
        `subjects_book_subjects`.`subject_id` = 1 
        AND T4.`subject_id` = 2 
        AND T6.`subject_id` = 3
    ) LIMIT 21; args=(1, 2, 3)
[<Book: Book object>]