Django数据映射(一对一,一对多,多对多)

class A(model.Model):
    ...
class B(model.Model):
    属性 = models.OneToOneField(A, on_delete=xxx)

# file : xxxxxxxx/models.py
from django.db import models

class Author(models.Model):
    '''作家模型类'''
    name = models.CharField('作家', max_length=50)

class Wife(models.Model):
    '''作家妻子模型类'''
    name = models.CharField("妻子", max_length=50)
    author = models.OneToOneField(Author, on_delete=models.CASCADE)  # 增加一对一属性 

from .models import *
author1 = Author.objects.create(name='王老师')
wife1 = Wife.objects.create(name='王夫人', author=author1)  # 关联王老师
author2 = Author.objects.create(name='小泽老师')  # 一对一可以没有数据对应的数据 

# 通过 wife 找 author
from .models import Wife
wife = Wife.objects.get(name='王夫人')
print(wife.name, '的老公是', wife.author.name)

# 通过 author.wife 关联属性 找 wife,如果没有对应的wife则触发异常
author1 = Author.objects.get(name='王老师')
print(author1.name, '的妻子是', author1.wife.name)
author2 = Author.objects.get(name='小泽老师')
try:
    print(author2.name, '的妻子是', author2.wife.name)
except:
    print(author2.name, '还没有妻子')

class A(model.Model):
    ...

class B(model.Model):
    属性 = models.ForeignKey("一"的模型类, on_delete=xx)

# file: otm/models.py
from django.db import models

class Publisher(models.Model):
    '''出版社【一】'''
    name = models.CharField('名称', max_length=50, unique=True)

class Book(models.Model):
    '''书【多】'''
    title = models.CharField('书名', max_length=50)
    publisher = ForeignKey(Publisher, on_delete=models.CASCADE)

#先创建 '一' ，再创建 '多'
from .models import *
pub1 = Publisher.objects.create(name='清华大学出版社')
Book.objects.create(title='C++', publisher=pub1)
Book.objects.create(title='Java', publisher_id=1)

#高级创建 - 利用 反向属性
pub2 = Publisher.objects.create(name='北京大学出版社')
pub2.book_set.create(title='西游记')

通过 publisher 属性查询即可
​​​​​​​book.publisher
 
abook = Book.objects.get(id=1)
print(abook.title, '的出版社是:', abook.publisher.name)

# 通过出版社查询对应的书
pub1 = Publisher.objects.get(name='清华大学出版社')
books = pub1.book_set.all()  # 通过book_set 获取pub1对应的多个Book数据对象
#books = Book.objects.filter(publisher=pub1)  # 也可以采用此方式获取
print("清华大学出版社的书有:")
for book in books:
   print(book.title)

属性 = models.ManyToManyField(MyModel)

class Author(models.Model):
    ...

class Book(models.Model):
    ...
    authors = models.ManyToManyField(Author)

class Author(models.Model):
    '''作家模型类'''
    name = models.CharField('作家', max_length=50)
    def __str__(self):
        return self.name
    
class Book(models.Model):
    '''书模型类'''
    title = models.CharField('书名', max_length=50)
    authors = models.ManyToManyField(Author)
    def __str__(self):
           return self.title 

方案1 先创建 author 再关联 book
    author1 = Author.objects.create(name='吕老师')
    author2 = Author.objects.create(name='王老师')
    # 吕老师和王老师同时写了一本Python
    book11 = author1.book_set.create(title="Python")
    author2.book_set.add(book11) 
    
方案2 先创建 book 再关联 author
    book = Book.objects.create(title='python1')
    #郭小闹和吕老师都参与了 python1 的 创作
    author3 = book.authors.create(name='guoxiaonao')
    book.authors.add(author1)

author.book_set.all()
author.book_set.filter()