这里先来借用一个书本(book)的数据模型作为例子：
from django.db import modelsclass 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.nameclass 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()[<Author: Adrian Holovaty>, <Author: Jacob Kaplan-Moss>]>>> b.authors.filter(first_name='Adrian')[<Author: Adrian Holovaty>]>>> 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()[<Book: The Django Book>, <Book: Adrian's Other Book>]
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。
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