ManyToMany表中记录数的简单计数

Question

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)

我想我错过了一些非常明显的东西但是如何计算在这个多对多表中创建的记录数authors = models.ManyToManyField(Author)？

Answer 1

查看文档,它非常简单:

b = Book.objects.all()[0]
b.authors.count()

更新:

最初的问题是要求提供数据库中所有作者的列表,而不是查找每本书的作者列表.

要获取数据库中所有作者的列表:

Author.objects.count() ## Returns an integer.