多表设计
基表 my_utils/model.py
utils/model.py
from django.db import models
class BaseModel(models.Model):
create_time = models.DateTimeField(auto_now_add=True, null=True)
is_delete = models.BooleanField(default=False)
class Meta:
# 抽象表，不会完成数据库迁移
abstract = True
多表关系 api/models.py
模型：api/models.py
from django.db import models
from my_utils.model import BaseModel
# 断表的原因是：必须得有author 才有 authors
# Create your models here.
'''
Book 表： name price img
Author 表：name age
Author_detail 表：phone
Publish 表: name address
Book Author 多对多
Book Publish 多对一
Author Author_detail 一对一
'''
'''
总结就是一句话：断外键+设置逻辑级联删除方式+不影响链表操作
多表关系总结：
一对一：Author AuthorDetail两表
1）关系放在AthorDetail表中：作者删除详情删除，详情删除作者保留
2）作用找详情用 外键related_name(detail),详情找作者用 外键字段（author)
下面的设置一句话：断外键，orm依然可以链表操作，orm层面级联删除
author = models.OneToOneField(to=Author,null=True,related_name='detail',# 用于author表链表本表记录
db_constraint=False,# 断掉外键关系，但是orm可以进行链表操作。
on_delete=models.CASCADE # orm逻辑上进行级联删除
)
一对多：Book、Publish两表
1）关系字段应该放在Book表中（多的一方）：删除书 出版社保留， 出版社删 除书删掉（下面会解决）
2）出版社找书用 外键related_name(books),书找出版社 外键字段（publish）
----下面的设置一句话：断外键，orm依然可以链表操作，orm层面级联删除动作取消
publish = models.ForeignKey(to='Publish',null=True,
related_name='books', # 用于反向查询
db_constraint=False, # 断开外键
on_delete=models.DO_NOTHING # 级联删除无动作
)
外键字段的其它关联方式
1）断关联，删除关联表记录，外键值置空
db_constraint=False, on_delete=models.SET_NULL, null=True,
2）断关联，删除关联表记录，外键值置默认值
db_constraint=False, on_delete=models.SET_DEFAULT, default=1,
多对多：Book、Author两表
1）关系字段放在任意一方都可以：出版社删除或书删除彼此不影响，但关系表一定级联删除
2）正向找 外键字段，反向找 外键字段related_name
3）db_constraint断开表关联，多对多on_delete不存在(不设置，本质在第三张表中设置，且一定是级联)
authors = models.ManyToManyField(to='Author', null=True,
related_name='books',
db_constraint=False,
)
'''
class Book(BaseModel):
name = models.CharField(max_length=64,null=True)
price = models.DecimalField(max_digits=5,decimal_places=2,null=True)
img = models.ImageField(upload_to='img',default='img/default.png')
# 多对多
authors = models.ManyToManyField(to='Author',
# related_name = 'books',
# db_constraint = False,
)
# 多对一
publish = models.ForeignKey(to='Publish',null=True,
related_name='books', # 用于反向查询
db_constraint=False, # 断开外键
on_delete=models.DO_NOTHING # 级联删除无动作
)
class Meta:
db_table = 'lf_book'
verbose_name = '书籍'
verbose_name_plural =verbose_name
class Author(BaseModel):
name = models.CharField(max_length=64,null=True)
age = models.IntegerField(null=True)
class Meta:
db_table = 'lf_author'
verbose_name = '作者'
verbose_name_plural =verbose_name
# 一对一
class AuthorDetail(BaseModel):
author = models.OneToOneField(to=Author,null=True,related_name='detail',# 用于author表链表本表记录
db_constraint=False,# 断掉外键关系，但是orm可以进行链表操作。
on_delete=models.CASCADE # orm逻辑上进行级联删除
)
phone = models.CharField(max_length=11,null=True)
class Meta:
db_table = 'lf_author_detail'
verbose_name = '作者详情'
verbose_name_plural =verbose_name
class Publish(BaseModel):
name = models.CharField(max_length=64,null=True)
address = models.CharField(max_length=80,null=True)
class Meta:
db_table = 'lf_publish'
verbose_name = '出版社'
verbose_name_plural = verbose_name
测试代码：script/t_dg.py
import os
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "dg_proj.settings")
import django
django.setup()
from api import models
# 一对一
# author = models.Author.objects.first() # type: models.Author
# print(author.name)
# print(author.detail.mobile)
# author.delete()
# author_detail = models.AuthorDetail.objects.first() # type: models.AuthorDetail
# print(author_detail.mobile)
# print(author_detail.author.name)
# author_detail.delete()
# 一对多
# publish = models.Publish.objects.filter(pk=2).first() # type: models.Publish
# print(publish.name)
# print(publish.books.first().name)
# publish.delete()
# publish = models.Publish.objects.filter(is_delete=False).first() # type: models.Publish
# if publish:
# print(publish.name)
# print(publish.books.first().name)
# publish.is_delete = True
# publish.save()
# book = models.Book.objects.first() # type: models.Book
# print(book.name)
# print(book.publish.name)
# book.delete()
# 多对多
# book = models.Book.objects.first() # type: models.Book
# print(book.name)
# print(book.authors.first().name)
# book.delete()
author = models.Author.objects.first() # type: models.Author
print(author.name)
print(author.books.first().name)
author.delete()
