Django, one-to-many, many-to-many

时间：2022-10-04 14:11:13

1、定义关系

  • 定义三个表，Publisher，Book，Author

  • 一个作者有姓，有名及email地址。

  • 出版商有名称，地址，所在城市、省，国家，网站。

  • 书籍有书名和出版日期。 它有一个或多个作者（和作者是多对多的关联关系[many-to-many]）， 只有一个出版商（和出版商是一对多的关联关系[one-to-many]，也被称作外键[foreign key]）

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>]
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