# Many-To-Many Example : Authors vs Books

class Author(models.Model):

    name = models.CharField(max_length=20)

    def __unicode__(self):

        return self.name

class Book(models.Model):

    name = models.CharField(max_length=20)

    authors = models.ManyToManyField(Author)

    def __unicode__(self):

        return self.name

[root@bogon csvt03]#  py manage.py syncdb

Creating tables ...

Creating table blog_author

Creating table blog_book_authors   <--- 多对多映射表

Creating table blog_book

Installing custom SQL ...

Installing indexes ...

Installed 0 object(s) from 0 fixture(s)

[root@bogon csvt03]#  ipython manage.py shell

In [1]: from blog.models import  Author , Book

In [2]: au1 = Author(name='Author-1')

In [3]: au2 = Author(name='Author-2')

In [4]: au3 = Author(name='Author-3')

In [5]: au4 = Author(name='Author-4')

In [6]: b1=Book(name='Book-1')

In [7]: b1.save()       <--- 必须先生成数据库实例才能添加多对多关系

In [8]: au1.save()      <--- 必须先生成数据库实例才能添加多对多关系

In [9]: au2.save()      <--- 必须先生成数据库实例才能添加多对多关系

In [10]: au3.save()     <--- 必须先生成数据库实例才能添加多对多关系

In [11]: au4.save()     <--- 必须先生成数据库实例才能添加多对多关系

In [12]: b1.authors.add(au1,au2)                     <--- 添加多对多关系

In [13]: b1.authors.all()

Out[13]: [<Author: Author-1>, <Author: Author-2>]

In [14]:  b1.authors.filter(name__exact='Author-2')

Out[14]: [<Author: Author-2>]

In [15]: au1.book_set.all()                          <--- 多对多关系反向查询

Out[15]: [<Book: Book-1>]

In [16]: au3.book_set.add(b1)                        <--- 多对多关系反向添加

In [17]: b1.authors.all()

Out[17]: [<Author: Author-1>, <Author: Author-2>, <Author: Author-3>]

In [18]: au4.book_set.create(name='Book Newly Created') <--- 创建并添加多对多关系

Out[18]: <Book: Book Newly Created>

In [19]: au4.book_set.all()

Out[19]: [<Book: Book Newly Created>]

In [20]: au2.book_set.all()

Out[20]: [<Book: Book-1>]

In [21]: au2.book_set.remove(b1)                     <--- 移除关系

In [22]: au2.book_set.all()

In [23]: