django基础三

表结构的设计(多对多)

class Book(models.Model):
    title = models.CharField(max_length=32)
    pub = models.ForignKey('Publisher',on_delete=models.CASCADE)
    
    
class Author(models.Model):
    name = models.CharField(max_length=32)
    books = models.ManyToManyField('book') #描述多对多关系,不生成字段生成关系表

 

查询

all_authors = models.Author.objects.all9).order_by('id')
​
for author in all_authors:
    print(author)
    print(author.name)
    print(author.pk)
    print(author.books) #关系管理对象
    print(author.books.all())  #所关联的所有对象
    print('*'*32)

 

新增

books = requrst.POST.getlist('books')  #获取多个元素
​
#新建作者
author_obj = models.Author.create(name=name)
#给作者和书籍绑定关系
author_obj.books.set(books)  #[id,id]

 

创建多对多的表的方法

1.django通过ManyToManyField自动创建第三张表

class Book(models.Model):
    title = models.CharField(max_length=32)
    pub = models.ForeignKey('Publisher',on_delete=models.CASCADE)
    #author = models.ManyToManyField('Author') #描述多对多关系不生成字段生成关系表
    
    def __repr__(self):
        return self.title
    
    __str__ = __repr__
    
    
class Author(models.Model):
    name = models.CharField(max_length=32)
    books = models.ManyToManyField('Book') #描述多对多关系,不生成字段生成关系表
2 自己手动创建第三张表

class Book(models.Model):
    title = models.CharField(max_length=32)
    
    
class Author(models.Model):
    name = models.CharField(max_length=32)
    
    
class Book_Author(models.Model):
    book = models.ForeignKey(Book,on_delete=models.CASCADE)
    author = models.ForeignKey(Author,on_delete=models.CASCADE)
    date = models.DateField()
3.自己创建 + ManyToManyField

class Book(models.Model):
    title = models.CharField(max_length=32)
    
​
class Author(models.Model):
    name = models.CharField(max_length=32)
    books = models.ManyToManyField(Book,through='Book_Author',through_fields=['author','book'])
    
    
class Book_Author(models.Model):
    book = models.ForeignKey(Book,on_delete=models.CASCADE)
    author = models.ForeignKey(Author,on_delete=models.CASCADE)
    date = models.DateField()