ManyToMany表中记录数的简单计数

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)

I think I'm missing something really obvious but how do I get a count for the number of records created in this many-to-many table authors = models.ManyToManyField(Author)?

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= models.ManyToManyField（作者）？

1 个解决方案

#1

Check out the docs, it's pretty simple:

查看文档，它非常简单：

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

Update:

更新：

The original question was asking for a list of all of the Authors in the database, not looking for a list of authors per book.

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。

To get a list of all of the authors in the database:

要获取数据库中所有作者的列表：

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

#1