from django.db import models

class Publisher(models.Model):
 name = models.CharField(max_length=30)
 address = models.CharField(max_length=50)
 city = models.CharField(max_length=60)
 state_province = models.CharField(max_length=30)
 country = models.CharField(max_length=50)
 website = models.URLField()

 def __unicode__(self):
 return self.name

class Author(models.Model):
 first_name = models.CharField(max_length=30)
 last_name = models.CharField(max_length=40)
 email = models.EmailField()

 def __unicode__(self):
 return u'%s %s' % (self.first_name, self.last_name)

class Book(models.Model):
 title = models.CharField(max_length=100)
 authors = models.ManyToManyField(Author)
 publisher = models.ForeignKey(Publisher)
 publication_date = models.DateField()

 def __unicode__(self):
 return self.title

访问多对多值(Many-to-Many Values)

多对多和外键工作方式相同，只不过我们处理的是QuerySet而不是模型实例。 例如,这里是如何查看书籍的作者：

>>> b = Book.objects.get(id=50)
>>> b.authors.all()
[, ]
>>> b.authors.filter(first_name='Adrian')
[]
>>> b.authors.filter(first_name='Adam')
[]

反向查询也可以。 要查看一个作者的所有书籍,使用author.book_set ,就如这样:

>>> a = Author.objects.get(first_name='Adrian', last_name='Holovaty')
>>> a.book_set.all()
[, ]

这里,就像使用 ForeignKey字段一样，属性名book_set是在数据模型(model)名后追加_set。