09 ORM 多表操作，创建表

1、数据库表关系

　　1.一对多

为什么需要，重复字段太多

一对多关系表

Book
    id  title   price   publish_id
    1   python  100         1
    2   php     200         2
    3   go      100         1
    4   java    300         1


Publish
    id  name        email       addr
    1   人民出版社   123@qq.com  北京
    2   南京出版社   456@qq.com  南京


#总结：一旦确定表关系是一对多：在多对应的表中创建关联字段,publish_id

   #查询python这本书的出版社的邮箱（子查询）
    select Publish.email from Publish where Publish.id = ()
    select Book.publish_id from Book where Book.title='python'

2.多对多

Book
    id  title   price   publish_id
    1   python  100         1
    2   php     200         2
    3   go      100         1
    4   java    300         1


Author
    id  name    age     addr
    1   alex    34      beijing
    2   jack    33      nanjing


Book2Author
    id  book_id author_id
    1       2       1
    2       2       2
    3       3       2

# 总结：一旦确定表关系是多对多：创建第三张表
    Book2Author
            id  book_id author_id

# alex出版过的书籍名称（子查询）
select Book.title from Book where Book.id in ()
select Book2Author.book_id where author_id = ()
select Author.id from Author where Author.name='alex'

　　3.一对一

Author
    id  name    age     ad_id(unique)   id  addr        gender  tel     gf_name
    1   alex    34          1           1   beijing     male    110     小花
    2   jack    33          2           2   nanjing     female  999     红娘

# 为了解耦


#方式1：
Author
    id  name    age     ad_id(unique)
    1   alex    34          1
    2   jack    33          2

AuthorDetail
    id  addr        gender  tel     gf_name
    1   beijing     male    110     小花
    2   nanjing     female  999     红娘


#方式2：
Author
    id  name    age
    1   alex    34
    2   jack    33

AuthorDetail
    id  addr        gender  tel     gf_name     author_id(unique)
    1   beijing     male    110     小花              1
    2   nanjing     female  999     红娘              2

#总结：一旦确定关系为一对一：在两张表中的任意一张表中建立关联字段+Unique

2、sql语句创建关联表

Publish
Book
Author
Book2Author
AuthorDetail

　　

create table publish(
                    id int primary key auto_increament,
                    name varchar(20)
                    );

create table book(
                id int primary key auto_increament,
                title varchar(20),
                price decimal(8,2),
                pub_date date,
                publish_id int,
                foreign key(publish_id) references publish(id)
                );

create table authordetail(
                id int primary key auto_increament,
                tel varchar(20),
                );

create table author(
                id int primary key auto_increament,
                name varchar(20),
                age int,
                authordetail_id int unique,
                foreign key(authordetail_id) references authordetail(id)
                );

create table Book2Author(
                id int primary key auto_increament,
                book_id int,
                author_id int,
                foreign key(book_id) references book(id),
                foreign key(author_id) references author(id)
                );

3、ORM生成关联表模型

 一对一

"""
1对1  author
create table author(
                id int primary key auto_increament,
                name varchar(20),
                age int,
                authordetail_id int unique,
                foreign key(authordetail_id) references authordetail(id)
                );
create table authordetail(
                id int primary key auto_increament,
                tel varchar(20),
                );
"""

# 作者表
class Author(models.Model):
    nid = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    age = models.IntegerField()

    # 1对1
    # authordeatil = models.OneToOneField(to=AuthorDetail, to_field=nid)        # 如果AuthorDetail表在后面定义也可以找到
    # authordeatil = models.OneToOneField(to="AuthorDetail", to_field="nid")      # 推荐使用字符串格式，    # django2.0 会报错，级联删除 
    authordeatil = models.OneToOneField(to="AuthorDetail", to_field="nid", on_delete=models.CASCADE)     


# 作者详情表
class AuthorDetail(models.Model):
    nid = models.AutoField(primary_key=True)
    birthday = models.DateField()
    telephone = models.BigIntegerField()
    addr = models.CharField(max_length=32)

一对多、多对多

"""
一对多   Book -- Publish
create table publish(
                    id int primary key auto_increament,
                    name varchar(20)
                    );

create table book(
                id int primary key auto_increament,
                title varchar(20),
                price decimal(8,2),
                pub_date date,
                publish_id int,
                foreign key(publish_id) references publish(id)
                );
"""
# 出版社表
class Publish(models.Model):
    nid = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    city = models.CharField(max_length=32)
    email = models.EmailField()

# 书籍表
class Book(models.Model):
    nid = models.AutoField(primary_key=True)
    title = models.CharField(max_length=32)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    publishDate = models.DateField()

    # 1对多关系
    # publish = models.ForeignKey(to=Publish, to_field='nid')  # django2.0 会报错，级联删除
    publish = models.ForeignKey(to=Publish, to_field='nid', on_delete=models.CASCADE)

    # 多对多
    authors = models.ManyToManyField(to="Author")  #  manytomany不会报错级联删除
    """
    多对多  Book----  Book2Author ---- Author

    create table Book2Author(
                    id int primary key auto_increament,
                    book_id int,
                    author_id int,
                    foreign key(book_id) references book(id),
                    foreign key(author_id) references author(id)
                    );
    """

 

多对多可以 继续定义Book2Author， 推荐使用ORM的 ManyToManyField

4、生成数据库表

级联删除错误

C:\PycharmProjects\ORM2>python manage.py makemigrations
Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "C:\PycharmProjects\ORM2\app01\models.py", line 72, in <module>
    class Author(models.Model):
  File "C:\PycharmProjects\ORM2\app01\models.py", line 79, in Author
    authordeatil = models.OneToOneField(to="AuthorDetail", to_field="nid")     
TypeError: __init__() missing 1 required positional argument: 'on_delete'

# 级联删除字段  on_delete=models.CASCADE    一对多 一对一
publish = models.ForeignKey(to=Publish, to_field='nid', on_delete=models.CASCADE)
authordeatil = models.OneToOneField(to="AuthorDetail", to_field="nid", on_delete=models.CASCADE)
# authors = models.ManyToManyField(to="Author")  多对多 不会报错

python manage.py makemigrations
python manage.py migrate

注意事项：

•  表的名称myapp_modelName，是根据 模型中的元数据自动生成的，也可以覆写为别的名称　　
•  id 字段是自动添加的
•  对于外键字段，Django 会在字段名上添加"_id" 来创建数据库中的列名
•  这个例子中的CREATE TABLE SQL 语句使用PostgreSQL 语法格式，要注意的是Django 会根据settings 中指定的数据库类型来使用相应的SQL 语句。
•  定义好模型之后，你需要告诉Django _使用_这些模型。你要做的就是修改配置文件中的INSTALL_APPSZ中设置，在其中添加models.py所在应用的名称。
• 外键字段 ForeignKey 有一个 null=True 的设置(它允许外键接受空值 NULL)，你可以赋给它空值 None 。

5、多表操作 添加记录

url

from django.contrib import admin
from django.urls import path, re_path, include

urlpatterns = [
    path('admin/', admin.site.urls),
    re_path(r'^app01/', include(('app01.urls', 'app01')))
]

from django.urls import path, re_path, include

from app01 import views
urlpatterns = [
    re_path(r'^add/$', views.add, name='add')
]

 　　1.单表

from django.shortcuts import render,HttpResponse

# Create your views here.
from app01.models import *


def add(request):
    # 1.单表添加记录
    ret1 = Publish.objects.create(
        name='人民出版社',
        city='beijing',
        email='[email protected]',
    )
    ret2 = Publish.objects.create(
        name='南京出版社',
        city='nanjing',
        email='[email protected]',
    )
    print(ret2)     # Publish object (2)


    return HttpResponse('OK')

 

　　2.一对多

 

　　3、

6

4