标签：访问 RKE 对象 tom res count 存储 state mos
1、定义关系
定义三个表，Publisher，Book，Author
出版商有名称，地址，所在城市、省，国家，网站。
2、定义model
from django.db import models
class Publisher(models.Model):
name = models.CharField(max_length=30)
address = models.CharField(max_length=50)
city = models.CharField(max_length=60)
state_province = models.CharField(max_length=30)
country = models.CharField(max_length=50)
website = models.URLField()
class Author(models.Model):
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=40)
email = models.EmailField()
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
3、基本数据库访问
当你使用Django modle API创建对象时Django并未将对象保存至数据库内，除非你调用save() 方法
>>> from books.models import Publisher
>>> p1 = Publisher(name=‘Apress‘, address=‘2855 Telegraph Avenue‘,
... city=‘Berkeley‘, state_province=‘CA‘, country=‘U.S.A.‘,
... website=‘http://www.apress.com/‘)
>>> p1.save()
>>> p2 = Publisher(name="O‘Reilly", address=‘10 Fawcett St.‘,
... city=‘Cambridge‘, state_province=‘MA‘, country=‘U.S.A.‘,
... website=‘http://www.oreilly.com/‘)
>>> p2.save()
>>> publisher_list = Publisher.objects.all()
>>> publisher_list
[, ]
如果需要一步完成对象的创建与存储至数据库，就使用objects.create() 方法
>>> p1 = Publisher.objects.create(name=‘Apress‘, ... address=‘2855 Telegraph Avenue‘, ... city=‘Berkeley‘, state_province=‘CA‘, country=‘U.S.A.‘, ... website=‘http://www.apress.com/‘) >>> p2 = Publisher.objects.create(name="O‘Reilly", ... address=‘10 Fawcett St.‘, city=‘Cambridge‘, ... state_province=‘MA‘, country=‘U.S.A.‘, ... website=‘http://www.oreilly.com/‘) >>> publisher_list = Publisher.objects.all() >>> publisher_list
数据过滤
>>> Publisher.objects.filter(name=‘Apress‘) [<Publisher: Apress>]
>>> Publisher.objects.filter(country="U.S.A.", state_province="CA")
[<Publisher: Apress>]
>>> Publisher.objects.filter(name__contains="press")
[<Publisher: Apress>]
contains部分会被Django翻译成LIKE语句
获取单个对象
>>> Publisher.objects.get(name="Apress")
<Publisher: Apress>
排序
>>> Publisher.objects.order_by("name")
[<Publisher: Apress>, <Publisher: O‘Reilly>]
访问外键
>>> b = Book.objects.get(id=50)
>>> b.publisher
>>> b.publisher.website
u‘http://www.apress.com/‘
访问多对多
>>> b = Book.objects.get(id=50)
>>> b.authors.all()
[<Author: Adrian Holovaty>, <Author: Jacob Kaplan-Moss>]
>>> b.authors.filter(first_name=‘Adrian‘)
[<Author: Adrian Holovaty>]
>>> b.authors.filter(first_name=‘Adam‘)
[]
反向查询也可以。 要查看一个作者的所有书籍,使用author.book_set
>>> a = Author.objects.get(first_name=‘Adrian‘, last_name=‘Holovaty‘)
>>> a.book_set.all()
[<Book: The Django Book>, <Book: Adrian‘s Other Book>]
Django, one-to-many, many-to-many
标签：访问 RKE 对象 tom res count 存储 state mos
原文地址：https://www.cnblogs.com/gange111/p/9403409.html
