多对多字段的所有值:Django [英] All the values of the many to many field : Django

问题描述

我有两个模型:

class Author(models.Model);
    name = models.CharField(max_length=255)

class Book(models.Model):
    title = models.CharField(max_length=255)
    authors = models.ManyToManyField(Author, null=True, blank=True)

现在，我想要所有书籍的信息.所以，我做到了:

Now, I want the info of all the books. So, I did:

book_info = Book.objects.all().values('title', 'authors__name')

而且，它给出了这样的输出(对于有 2 个作者的 1 本书):

And, it gives an output like (for 1 book having 2 authors):

[{'title': u'book1', 'authors__name': u'author1'},{'title': u'book1', 'authors__name': u'author2'}]

我想要的是:

[{'title': u'book1', 'authors': [{'name':u'author1'},{'name':u'author2'}]}]

作者模型中可能有更多字段，因此也想获取这些字段.

I may have more fields in the author model, so would like to get those fields as well.

我可以在单个查询中执行此操作吗?

Can I do this in a single query?

我该怎么做才能得到想要的结果?

What can I do to get something like the desired result?

推荐答案

Django 1.4

好问题，使用prefetch_related:

In [3]: [{'name': b.name, 'authors': [a.name for a in b.authors.all()]} for b in Book.objects.prefetch_related('authors')]
(0.000) SELECT "test_app_book"."id", "test_app_book"."name" FROM "test_app_book"; args=()
(0.000) SELECT ("test_app_book_authors"."book_id") AS "_prefetch_related_val", "test_app_author"."id", "test_app_author"."name" FROM "test_app_author" INNER JOIN "test_app_book_authors" ON ("test_app_author"."id" = "test_app_book_authors"."author_id") WHERE "test_app_book_authors"."book_id" IN (1, 2); args=(1, 2)
Out[3]: 
[{'authors': [u'a', u'b'], 'name': u'book'},
 {'authors': [u'b'], 'name': u'test'}]

Django 1.3

prefetch_related 是在 Django 1.4 中引入的.对于 Django 1.3，您需要 django-selectreverse:

In [19]: [{'name': b.name, 'authors': [a.name for a in b.authors_prefetch]} for b in Book.objects.select_reverse({'authors_prefetch': 'authors'})]
(0.000) SELECT "test_app_book"."id", "test_app_book"."name" FROM "test_app_book"; args=()
(0.001) SELECT (test_app_book_authors.book_id) AS "main_id", "test_app_author"."id", "test_app_author"."name" FROM "test_app_author" INNER JOIN "test_app_book_authors" ON ("test_app_author"."id" = "test_app_book_authors"."author_id") WHERE "test_app_book_authors"."book_id" IN (1, 2); args=(1, 2)
Out[19]: 
[{'authors': [u'a', u'b'], 'name': u'book'},
 {'authors': [u'b'], 'name': u'test'}]

使用 django-selectreverse:

class Book(models.Model):
    name = models.CharField(max_length=100)
    authors = models.ManyToManyField(Author, null=True, blank=True)

    objects = ReverseManager()

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