所有的价值观许多到很多领域：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，我想要的信息所有的书。所以，我做了：

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

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

而且，它给出一个输出（对于1本有2个作者的书）：

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'}]}]

我可能在作者模型中有更多的字段，所以喜欢获得这些字段。

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?

做某事像想要的结果？

推荐答案

Django 1.4

很好的问题，请使用 pr efetch_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在Django 1.4中引入。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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