Django---(五)

多对多

表结构的设计

class Book(models.Model):
    title = models.CharField(max_length=32)
    pub = models.ForeignKey('Publisher', on_delete=models.CASCADE)


class Author(models.Model):
    name = models.CharField(max_length=32)
    books = models.ManyToManyField('Book')  # 描述多对多的关系  不生成字段  生成关系表

查询

all_authors = models.Author.objects.all().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 = request.POST.getlist('books')   # 获取多个元素

# 新建作者
author_obj = models.Author.objects.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)
    # authors = models.ManyToManyField('Author')  # 描述多对多的关系   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')  # 描述多对多的关系   不生成字段  生成关系表

2. 自己手动创建

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')


class Book_Author(models.Model):
    book = models.ForeignKey(Book, on_delete=models.CASCADE)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    date = models.DateField()