django-关系映射
一对多
定义
语法
示例
模型类的创建
otm/models.py
from django.db import models
# Create your models here.
class Publisher(models.Model):
name=models.CharField('出版社',max_length=20)
class Book(models.Model):
title=models.CharField('书名',max_length=11)
publisher=models.ForeignKey(Publisher, on_delete=models.CASCADE)
数据库显示内容
mysql> desc otm_book;
+--------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| title | varchar(11) | NO | | NULL | |
| Publisher_id | int | NO | MUL | NULL | |
+--------------+-------------+------+-----+---------+----------------+
3 rows in set (0.40 sec)
mysql> desc otm_publisher;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
mysql> show create table otm_book;
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
---+
| Table | Create Table
|
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
---+
| otm_book | CREATE TABLE `otm_book` (
`id` int NOT NULL AUTO_INCREMENT,
`title` varchar(11) NOT NULL,
`Publisher_id` int NOT NULL,
PRIMARY KEY (`id`),
KEY `otm_book_Publisher_id_4ca7afa5_fk_otm_publisher_id` (`Publisher_id`),
CONSTRAINT `otm_book_Publisher_id_4ca7afa5_fk_otm_publisher_id` FOREIGN KEY (`
Publisher_id`) REFERENCES `otm_publisher` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+----------+--------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
---+
1 row in set (0.05 sec)
mysql>
数据创建
shell
In [5]: p1=Publisher(name='南京大学出版社')
In [6]: p1.save()
In [7]: Book.objects.create(title='java',publisher=p1)
Out[7]: <Book: Book object (1)>
In [8]: p2=Pubilisher.objects.create(name='杭州大学出版社')
In [10]: Book.objects.create(title='java',publisher_id=2)
Out[10]: <Book: Book object (2)>
In [11]: Book.objects.create(title='django',publisher=p2)
Out[11]: <Book: Book object (3)>
数据查询
正向查询
In [19]: book1=Book.objects.get(id='1')
In [20]: book1.publisher.name
Out[20]: '南京大学出版社'
反向查询 注意是类名小写加一个下划线set（如 book_set）
In [38]: pub2=Publisher.objects.get(id=4)
In [39]: pub2.name
Out[39]: '杭州大学出版社'
In [40]: pub2.book_set.all()
Out[40]: <QuerySet [<Book: Book object (3)>]>
In [42]: pub2.book_set.all().title
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-42-be1e4f3f46eb> in <module>
----> 1 pub2.book_set.all().title
AttributeError: 'QuerySet' object has no attribute 'title'
In [43]: for i in pub2.book_set.all():
...: print(i.title)
...:
django
多对多
表的创建
mtm/models.py
from django.db import models
# Create your models here.
class Author(models.Model):
name=models.CharField('姓名',max_length=11)
class Book(models.Model):
title=models.CharField('书名',max_length=11)
author=models.ManyToManyField(Author)
mysql> desc mtm_author;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| name | varchar(11) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> desc mtm_book;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| title | varchar(11) | NO | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> desc mtm_book_author;
+-----------+------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| book_id | int | NO | MUL | NULL | |
| author_id | int | NO | MUL | NULL | |
+-----------+------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
数据创建
In [1]: from mtm.models import Book,Author
In [2]: author1=Author.objects.create(name='吕老师')
In [3]: author2=Author.objects.create(name='王老师')
In [4]: book1=author1.book_set.create(title='python')
In [5]: author2.book_set.add(book1)
In [7]: #先创建book,再关联author
In [8]: book2=Book.objects.create(title='django')
In [9]: #关联两个老师
In [10]: author3=book2.author.create(name='李老师')
In [11]: #再关联一位老师
In [12]: author3
Out[12]: <Author: Author object (3)>
In [13]: book2.author.add(author1)
In [14]: book2
Out[14]: <Book: Book object (2)>
数据查询
