Fourth, the introduction and use of relational tables Django learning

Introduction and use of relational tables

One relationship

xx = models.OneToOneField(to='表名',to_field='字段名',on_delete=models.CASCADE)  
#on_delete:删除时的一些级联效果,to_field可以不写,默认是关联到另一张表的主键,on_delete在1.x版本的django中不用写,默认是级联删除的,2.x版本的django要写.

Increased data

Mode 1

new_author_detail = models.AuthorDetail.objects.create(
        birthday='1979',
        telephone='138',
        addr='black'
    )
    # 方式1
    models.Author.objects.create(
        name='王涛',
        age=18,
        #直接将对象赋值属性
        authorDetail=new_author_detail 
    )

Mode 2

new_author_detail = models.AuthorDetail.objects.create(
        birthday='1979',
        telephone='138',
        addr='black'
    )
    # 方式2
    models.Author.objects.create(
        name='王涛',
        age=18,
        authorDetail_id=new_author_detail.id
    )

delete data

A foreign key to a table associated with Table II, Table deleted, without affecting the Table 2, Table 2 Table 1 affect delete

models.AuthorDetail.objects.get(id=2).delete()
models.Author.objects.get(id=3).delete()

update data

models.Author.objects.filter(id=5).update(
        name='崔老师',
        age=16,
        authorDetail=models.AuthorDetail.objects.get(id=5),
        authorDetail_id=4,
     )

Many relationship

xx = models.ForeignKey(to='表名',to_field='字段名',on_delete=models.CASCADE)

Increased data

Mode 1

Direct assignment as a foreign key to an object

obj = models.Publish.objects.get(id=1)
models.Book.objects.create(
    title='李帅',
    publishDate='2019-07-22',
    price=3,
    publishs=obj
)

Mode 2

obj = models.Publish.objects.get(id=1)
models.Book.objects.create(
        title='李帅test',
        publishDate='2019-07-22',
        price=3.5,
        publishs_id=1 #可以是整型，也可以是对象的属性（id）
        #publishs_id=obj.id
    )

delete data

models.Publish.objects.get(id=1).delete()
models.Book.objects.get(nid=1).delete()

update data

models.Book.objects.filter(pk=4).update(
title='B哥的往事2',
publishs=models.Publish.objects.get(id=3),
publishs_id=3, #注意级联关系 不能乱改
    )

Many relationship

xx = models.ManyToManyField(to='另外一个表名') #这是自动创建第三表

adding data

book_obj = models.Book.objects.get(nid=1)
    book_obj.authors.add(*[1,2])

delete data

book_obj = models.Book.objects.get(nid=6)
book_obj.authors.remove(6)#将某个特定的对象从被关联对象集合中去除。
book_obj.authors.remove(*[5,6])
book_obj.authors.clear() #情况与nid 6相关联的所有
book_obj.authors.add(*[1,])#添加表记录
book_obj.authors.set('1')#先清空然后在设置
book_obj.authors.set(['5','6']) #删除然后更新

Examples

from django.db import models

# Create your models here.

from django.db import models

# Create your models here.
#作者表
class Author(models.Model): #比较常用的信息放到这个表里面
    name=models.CharField( max_length=32)
    age=models.IntegerField()
    # authorDetail=models.OneToOneField(to="AuthorDetail",to_field="nid",on_delete=models.CASCADE)
    authorDetail=models.OneToOneField(to='AuthorDetail')  #一对一到AuthorDetail表  生成为表字段之后,会自动变为authorDetail_id这样有一个名称

    # 外键字段 -- 外键字段名_id

    # foreign+unique

    def __str__(self):
        return self.name

#作者详细信息表
class AuthorDetail(models.Model):
    birthday=models.DateField()
    # telephone=models.BigIntegerField()
    telephone=models.CharField(max_length=32)
    addr=models.CharField( max_length=64)
    def __str__(self):
        return self.addr


#出版社表   和 书籍表 是 一对多的关系
class Publish(models.Model):
    name=models.CharField( max_length=32)
    city=models.CharField( max_length=32)
    email=models.EmailField()  #charfield -- asdfasdf
    def __str__(self):
        return self.name

#书籍表
class Book(models.Model):
    nid = models.AutoField(primary_key=True)
    title = models.CharField( max_length=32)
    publishDate=models.DateField()
    price=models.DecimalField(max_digits=5,decimal_places=2)  #decimal(16,2)
    publishs=models.ForeignKey(to="Publish")
    authors=models.ManyToManyField(to='Author',)

    def __str__(self):
        return self.title