django-关系映射 一对一 一对多 多对多

关系映射

什么是关系映射

• 怎么建表
• 怎么传入数据
• 怎么查询数据

一对一的映射 on_delete

官网链接
cascade 是在orm层面进行设置
models.protect mysql默认

实例说明

models生成

oto.models.py

from django.db import models

# Create your models here.
class Author(models.Model):
    name=models.CharField('姓名',max_length=11)

class Wife(models.Model):
    name=models.CharField('姓名',max_length=11)
    author=models.OneToOneField(Author,on_delete=models.CASCADE)
    

迁移

E:django_video_studymysite2>python manage.py startapp oto
<class 'list'>

E:django_video_studymysite2>python manage.py makemigrations
<class 'list'>
Migrations for 'bookstore':
  bookstoremigrations006_auto_20210813_1917.py
    - Change Meta options on book
    - Alter field pub on book
Migrations for 'oto':
  otomigrations001_initial.py
    - Create model Author
    - Create model Wife

E:django_video_studymysite2>python manage.py migrate
<class 'list'>
Operations to perform:
  Apply all migrations: admin, auth, bookstore, contenttypes, oto, sessions
Running migrations:
  Applying bookstore.0006_auto_20210813_1917... OK
  Applying oto.0001_initial... OK

E:django_video_studymysite2>

数据库内样式

mysql> desc oto_wife;
+-----------+-------------+------+-----+---------+----------------+
| Field     | Type        | Null | Key | Default | Extra          |
+-----------+-------------+------+-----+---------+----------------+
| id        | int         | NO   | PRI | NULL    | auto_increment |
| name      | varchar(11) | NO   |     | NULL    |                |
| author_id | int         | NO   | UNI | NULL    |                |
+-----------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> show create table oto_wife;
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table                                                                                                                                                                                                                                                                                                                                     |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| oto_wife | CREATE TABLE `oto_wife` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(11) NOT NULL,
  `author_id` int NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `author_id` (`author_id`),
  CONSTRAINT `oto_wife_author_id_3d57c7a2_fk_oto_author_id` FOREIGN KEY (`author_id`) REFERENCES `oto_author` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

创建数据

In [1]: from oto.models import Author,Wife

In [2]: author1=Author.objects.create(name='王老师')

In [3]: #通过类的属性名创建数据

In [4]: wife1=Wife.objects.create(name='王夫人',author=author1)
mysql> select  *  from oto_wife;
+----+-----------+-----------+
| id | name      | author_id |
+----+-----------+-----------+
|  1 | 王夫人    |         1 |
+----+-----------+-----------+


In [5]: #通过外键字段名创建数据

In [6]: author2=Author.objects.create(name='果子哥')

In [7]: wife2=Wife.objects.create(name='郭老师',author_id=2)
mysql> select  *  from oto_wife;
+----+-----------+-----------+
| id | name      | author_id |
+----+-----------+-----------+
|  1 | 王夫人    |         1 |
|  2 | 郭老师    |         2 |
+----+-----------+-----------+
2 rows in set (0.00 sec)

数据查询

正向查询

In [7]: wife2=Wife.objects.create(name='郭老师',author_id=2)

In [8]: # 正向查询

In [9]: wife2
Out[9]: <Wife: Wife object (2)>

In [10]: wife2.author
Out[10]: <Author: Author object (2)>

In [11]: wife2.author.name
Out[11]: '果子哥'

反向查询

In [12]: # 反向查询

In [13]: # Author在onetoone中会有一个反向属性

In [14]: author1
Out[14]: <Author: Author object (1)>

In [15]: author1.wife.name
Out[15]: '王夫人'