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

访问外键(Foreign Key)值

当你获取一个ForeignKey 字段时,你会得到相关的数据模型对象。 例如:

>>> b = Book.objects.get(id=50)
>>> b.publisher

>>> b.publisher.website
u'http://www.apress.com/'

对于用`` ForeignKey`` 来定义的关系来说，在关系的另一端也能反向的追溯回来，只不过由于不对称性的关系而稍有不同。 通过一个`` publisher`` 对象，直接获取 books ，用 publisher.book_set.all() ，如下：

>>> p = Publisher.objects.get(name='Apress Publishing')
>>> p.book_set.all()
[, , ...]

实际上，book_set 只是一个 QuerySet，所以它可以像QuerySet一样,能实现数据过滤和分切，例如：

>>> p = Publisher.objects.get(name='Apress Publishing')
>>> p.book_set.filter(name__icontains='django')
[, ]

属性名称book_set是由模型名称的小写(如book)加_set组成的。