多对多表关系的三种创建方式

全自动:利用orm自动创建第三张关系表

缺点:扩展性差

1     class Book(models.Model):
2         name = models.CharField(max_length=32)
3         authors = models.ManyToManyField(to='Author')
4     class Author(models.Model):
5         name = models.CharField(max_length=32)

纯手动:

缺点:无法使用部分orm方法:add,set,remove,clear,正反向查询等

1     class Book(models.Model):
2         name = models.CharField(max_length=32)
3     
4     class Author(models.Model):
5         name = models.CharField(max_length=32)
6   
7     class Book2Author(models.Model):
8         book_id = models.ForeignKey(to='Book')
9         author_id = models.ForeignKey(to='Author')

半自动:(优先使用)

缺点:没法使用orm的add,set,remove,clear这四个方法

 1 class Book(models.Model):
 2     name = models.CharField(max_length=32)
 3     authors = models.ManyToManyField(to='Author',
 4                                      through='Book2Author',
 5                                      through_fields=('book','author')
 6                                      )
 7 class Author(models.Model):
 8     name = models.CharField(max_length=32)
 9     # books = models.ManyToManyField(to='Book',
10     #                                  through='Book2Author',
11     #                                  through_fields=('author','book')
12     #                                  )
13 class Book2Author(models.Model):
14     book = models.ForeignKey(to='Book')
15     author = models.ForeignKey(to='Author')

# through_fields字段先后顺序:当前表在前