python – Django ORM每位作者的书籍数量

概述class Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() friends = models.ManyToManyField('self', blank=True)class Publisher(models.Model): name =

class Author(models.Model):   name = models.CharFIEld(max_length=100)   age = models.IntegerFIEld()   frIEnds = models.ManyToManyFIEld('self',blank=True)class Publisher(models.Model):   name = models.CharFIEld(max_length=300)   num_awards = models.IntegerFIEld()class Book(models.Model):   isbn = models.CharFIEld(max_length=9)   name = models.CharFIEld(max_length=300)   pages = models.IntegerFIEld()   price = models.DecimalFIEld(max_digits=10,decimal_places=2)   rating = models.floatFIEld()   authors = models.ManyToManyFIEld(Author)   publisher = models.ForeignKey(Publisher)   pubdate = models.DateFIEld()class Store(models.Model):   name = models.CharFIEld(max_length=300)   books = models.ManyToManyFIEld(Book)

我想知道有多少本书是针对作者注册的.
比方说,我有作者A1,A2,A3.

一本书可能属于多位作者.
我有书,B1,B2,B3

我想知道有多少作者A1的书.让我说他属于2本书.

已经尝试过

Author.objects.all()Books.objects.filter(authors=43).count()2

哪一个更好？

for auth in authors:  book.count =book.book_auths.count()  book_counts_alternative_way = Book.objects.annotate(num_count=Count('book_auths')).filter(book_auths=tech,num_count__gt=0)

还有其他很有效的方法吗？

解决方法 将related_name提供给

authors = models.ManyToManyFIEld(Author,related_name='book_auths')

然后

author = Author.objects.get(ID=43)auth_books = author.book_auths.all()#auth_books are all books which belong to one author

要么

author = Author.objects.get(ID=43)  books = Book.objects.filter(author=author)

将给出作者所属的所有书籍.

或者如果你想知道所有作者

authors = Authors.objects.all()books = Book.objects.filter(author__in=(x for x in authors))

为您提供所有在db中存在作者的书籍.

要知道多少：只需将.count()附加到结果查询集.

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