from django.db import models  

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 self.name  

    class Meta:  
        db_table = "author"       

class Book(models.Model):  
    title = models.CharField(max_length=200)  
    authors = models.ManyToManyField(Author)  

    def __unicode__(self):  
        return self.title  

    class Meta:  
        db_table = "book"    


访问多值：
一本书的所有作者：
b = Book.objects.get(id=50)
b.authors.all()
b.authors.filter(first_name='Adam')
反向也可以，一个作者的所有书：
a = Author.objects.get(id=1)
a.book_set.all()
给多对多字段添加值（添加多对多关系）：
a = Author.objects.get(id=1)
b = Book.objects.get(id=50)
b.authors.add(a)
从多对多字段中删除值（删除多对多关系）：

a = Author.objects.get(id=1)
b = Book.objects.get(id=50)
b.authors.remove(a) 或者 b.authors.filter(id=1).delete()