举例讲解Django中数据模型访问外键值的方法-Python Tutorial-php.cn

举例讲解Django中数据模型访问外键值的方法

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Release： 2016-06-10 15:08:57

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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

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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/'

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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>, ...]

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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>]

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属性名称book_set是由模型名称的小写(如book)加_set组成的。

Related labels：

django data model

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