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Django REST 框架详解 03 | 模型建立与表设计



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)​

Django REST  框架详解 03 |  模型建立与表设计_后端

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

Django REST  框架详解 03 |  模型建立与表设计_后端_02

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

Django REST  框架详解 03 |  模型建立与表设计_数据库_03

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
Django REST  框架详解 03 |  模型建立与表设计_数据库_04
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
Django REST  框架详解 03 |  模型建立与表设计_数据库_05

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
Django REST  框架详解 03 |  模型建立与表设计_python_06

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

启动项目,登录

​​

​​

​​

Django REST  框架详解 03 |  模型建立与表设计_django_07



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