Django—模型对应关系（一对多）

目录

1. 模型
2. 增加
3. 删除，更新
4. 正反向查询
5. 跨关系查询

---

1. 模型

   ---

   #⼀个出版社可以出版多本书，⼀本书只能被⼀个出版社出版。出版社和图书表属于
   #⼀对多，⼀对多⼀般将主表中的主键并到从表中做外键。在模型中⽤ForeignKey表示多对⼀
   
   class Publisher(models.Model):
    pname = models.CharField(max_length=100,null=True)
    def __str__(self):
    return self.pname
    class Meta:
    db_table = 'publisher'
   class Book(models.Model):
    bname = models.CharField(max_length=200,null=True)
    #多对⼀模型通过ForeignKey表示多对⼀
    #如果publisher定义在book之后，第⼀个参数应该⽤字符串'Publisher'
    publisher = models.ForeignKey(Publisher,on_delete=models.CASCADE,
    null=True,
    db_column='pid', #表中字段名
    related_name='books') #通过出版社
   查图书时使⽤的关系名
    def __str__(self):
    return self.bname
    class Meta:
    db_table = 'book'

2. 增加

   ---

   
   # 增加
   pub = Publisher.objects.first()
   pub.books.create(bname='红岩')
   book = Book.objects.get(pk=1)
   pub.books.add(book) #book必须已经保存到数据库
   books = Book.objects.filter(pk__lt=5)
   pub.books.bulk_create(list(books))

3. 删除，更新

   ---

   pub = Publisher.objects.first()
   pub.books.all().delete() #删除出版社出版的所有图书
   pub.books.all().update(bname='ddd')

4. 正反向查询

   ---

   # 正向查询
   def findpublisher(req):
    pub = Publisher.objects.first()
    print(pub)
    # pub = Publisher()
    book = pub.book_set.all()
    print(book)
    return HttpResponse("查询出版社")
   
   
   # 反向查询
   def findbook(req):
    book = Book.objects.first()
    return HttpResponse(book.publisher.pname)

5. 跨关系查询

   ---

   def loopup(req):
    # 根据图书获取出版社
    pub = Publisher.objects.get(book__bname='花样年华927937')
    print(pub)
    # 根据出版社获取图书
    books = Book.objects.filter(publisher__pname='科技出版社5829')
    print(books)
    return HttpResponse("跨关系查询")