举例讲解Django中数据模型访问外键值的方法
先设置一个关于书本(book)的数据模型：
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 <Publisher: Apress Publishing> >>> 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() [<Book: The Django Book>, <Book: Dive Into Python>, ...]
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') [<Book: The Django Book>, <Book: Pro Django>]
属性名称book_set是由模型名称的小写(如book)加_set组成的。
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