文章目录
- 一、设计表
- 二、表关系
- 1.表关系设置
- 2.断开表关联
- 三、级联操作
- 1.CASCADE
- 2.SET_NULL
- 3.SET_DEFAULT
- 4.DO_NOTHING
- 四、Admin
一、设计表
假设需求,图书管理系统:
Book: name, price, img, authors, publish, is_delete, create_time
Publish: name, address, is_delete, create_time
Author: name, age, is_delete, create_time
AuthorDetail: mobile, author, is_delete, create_time
为什么要加 is_delete 字段?
- 只要入库的数据,永远不会被删除
- 如果主键 id 自增时,随便删除数据,会导致 id 不连续,查询时,会遗漏数据
- 只要该数据在入库了,就代表该数据有利用价值
为什么 Author, AuthorDetail 要拆分为两张表?
- Author 的查询频率高,如果字段太多会影响查询效率。AuthorDetail 只在需要详情时,才会用到
- 这两张表一般是一对一的关系
二、表关系
1.表关系设置
- Book - Publish:多对一
publish = models.ForeignKey(to='Publish', on_delete=models.CASCADE)
- Book - Author:多对多
authors = models.ManyToManyField(to='Author')
- Author - AuthorDetail:一对一
author = models.OneToOneField(to='Author', on_delete=models.CASCADE)
2.断开表关联
断关联:db_constraint=True
断开关联后,可以用编程逻辑来实现表的数据同步,这样会增加效率
class Book(BaseModel):
name = models.CharField(max_length=64)
price = models.DecimalField(max_digits=5, decimal_places=2)
img = models.ImageField(upload_to='img', default='img/default.jpg')
publish = models.ForeignKey(to='Publish', db_constraint=True, on_delete=models.CASCADE)
authors = models.ManyToManyField(to='Author')
class Meta:
db_table = 'book'
verbose_name = '书籍'
verbose_name_plural = verbose_name
def __str__(self):
return self.name
book 与 author 外键关系断开
class AuthorDetail(BaseModel):
mobile = models.CharField(max_length=11)
author = models.OneToOneField(
to='Author',
db_constraint=False, # 不断开表连接
on_delete=models.CASCADE, # 删除 AuthorDetail 不会影响 Author 表,但是如果删除 Author,AuthorDetail就会被一起删除
related_name='detail' # 正向查返回 name, 反向返回设置的 related_name
)
class Meta:
db_table = 'author_detail'
verbose_name = '作者详情'
verbose_name_plural = verbose_name
def __str__(self):
return f'{self.author}的详情'
author 与 author_detail 表关系断开
三、级联操作
1.CASCADE
models.py
class AuthorDetail(BaseModel):
mobile = models.CharField(max_length=11)
author = models.OneToOneField(
to='Author',
db_constraint=False,
related_name='detail',
on_delete = models.CASCADE,
)
class Meta:
db_table = 'author_detail'
verbose_name = '作者详情'
verbose_name_plural = verbose_name
def __str__(self):
return f'{self.author}的详情'
数据库迁移
python manage.py makemigrations
python manage.py migrrate
执行script.py
import os, django
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()
from api import models
models.AuthorDetail.objects.filter(pk=1).delete()
作者详情删除,并不会影响作者
执行
script.py
import os, django
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()
from api import models
models.Author.objects.filter(pk=1).delete()
反之,删除作者后,详情随之删除
2.SET_NULL
models.py
class AuthorDetail(BaseModel):
mobile = models.CharField(max_length=11)
author = models.OneToOneField(
to='Author',
db_constraint=False,
related_name='detail',
null=True,
on_delete=models.SET_NULL
)
class Meta:
db_table = 'author_detail'
verbose_name = '作者详情'
verbose_name_plural = verbose_name
def __str__(self):
return f'{self.author}的详情'
数据库迁移
python manage.py makemigrations
python manage.py migrrate
执行script.py
import os, django
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()
from api import models
models.Author.objects.filter(pk=1).delete()
作者删除后,作者详情保留,但是外键置空
3.SET_DEFAULT
- 作者删除,作者详情设置默认值:
on_delete=models.SET_DEFAULT
与 models.SET_NULL 相似,只是将空换为默认值
models.py
class AuthorDetail(BaseModel):
mobile = models.CharField(max_length=11)
author = models.OneToOneField(
to='Author',
db_constraint=False,
related_name='detail',
default='default',
on_delete=models.SET_DEFAULT
)
class Meta:
db_table = 'author_detail'
verbose_name = '作者详情'
verbose_name_plural = verbose_name
def __str__(self):
return f'{self.author}的详情'
4.DO_NOTHING
models.py
class AuthorDetail(BaseModel):
mobile = models.CharField(max_length=11)
author = models.OneToOneField(
to='Author',
db_constraint=False,
related_name='detail',
default='default',
on_delete=models.DO_NOTHING
)
class Meta:
db_table = 'author_detail'
verbose_name = '作者详情'
verbose_name_plural = verbose_name
def __str__(self):
return f'{self.author}的详情'
四、Admin
通过 Admin 我们可以直接通过后台来编辑表
admin.py
注册
from django.contrib import admin
from api import models
admin.site.register(models.Author)
admin.site.register(models.AuthorDetail)
admin.site.register(models.Book)
admin.site.register(models.Publish)
创建后台用户
manage.py@def_proj01 > createsuperuser
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