Django简单入门教程(三)模型 model


 

参考:《The Django Book》 第5章


1.setting.py 配置

 

 

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.', # 用什么数据库管理系统
        'NAME': '',                      # 数据库名称,如果用sqlite,要写完整路径
        'USER': '',                      # 如果用sqlite,这个不用写
        'PASSWORD': '',          # 如果用sqlite,这个不用写
        'HOST': '',                      # 告诉Django连接那一台. Not used with sqlite3. 如果用sqlite也空白
        'PORT': '',                      # 设置端口,空白就是默认,一般用默认的就行了。对于sqlite没用。
    }
}

 

 

'ENGINE' 可以有:

'ENGINE'                                                                 数据库管理系统         适配器           适配器下载地址

django.db.backends.postgresql_psycopg2            PostgreSQL               psycopg       http://www.djangoproject.com/r/python-pgsql/.

django.db.backends.mysql                                     MySQL                       MySQLdb     http://www.djangoproject.com/r/python-mysql/

django.db.backends.sqlite3                                   SQLite

django.db.backends.oracle                                    Oracle                         cx_Oracle    http://www.djangoproject.com/r/python-oracle/

注意:用那个DBMS,就要安装对应DBMS的适配器。SQLite的,python默认已经装好了。


可用下面来命令测试数据库配置,如果没有显示错误信息,配置就是正确的。

>>> from django.db import connection

>>> cursor = connection.cursor()


2.创建APP


project跟APP的区别:一个是配置,一个是代码。一个project可以包含很多app以及它们的配置。一个app是一套Django功能的集合,通常包括模型和视图,按python的包结构的方式存在。


前面你可以创建app,但是如果要用模型,你就必须创建一个app。模型必须放在apps中。


创建一个“books”模型

python manage.py startapp books

它会创建一个books包,内容如下

books/

├── admin.py

├── __init__.py

├── models.py

├── tests.py

└── views.py


然后在settings.py中INSTALLED_APPS中添加 'books',

 


3.定义模型,模型安装


例子:

在models.py 中添加

 

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()

 


 

Publisher模块相当于:

 

 

CREATE TABLE "books_publisher" (
    "id" serial NOT NULL PRIMARY KEY,
    "name" varchar(30) NOT NULL,
    "address" varchar(50) NOT NULL,
    "city" varchar(60) NOT NULL,
    "state_province" varchar(30) NOT NULL,
    "country" varchar(50) NOT NULL,
    "website" varchar(200) NOT NULL
);

 


 

注意:这里没有显示的为这些模型定义任何主键。除非指明,Django会自动为每个模型生成一个自增长的单独主键 id

 


 

可以用下面的命令验证模型的有效性

 

python manage.py validate

 


 

可以用下面命令生成SQL语句,它这只是生成SQL语句,不会执行

 

python manage.py sqlall books

 


 

如果想执行,执行下面语句(这个语句,在里添加新的模型或者app时才有用,修改删除模型syncdb不会做出任何反应

 

python manage.py syncdb

 



4.数据库操作


(1)数据库插入,显示

 


>>> from books.models import *

 

>>> 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

 

[<Publisher: Publisher object>, <Publisher: Publisher object>]

 


 

单单的p1=Publisher(...) 不会插入,必须要p1.save() 后才会真正生效

 


 

如果想一次性完成插入执行下面的命令

 

>>> from books.models import *

 

>>> 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

 

[<Publisher: Publisher object>, <Publisher: Publisher object>]

 


 

Publisher.objects.all()相当于 select

 

在输入publisher_list时,返回的对象名字都一样,不好分辨,解决方法就是,在模板类中添加__unicode__() 方法

 

如:

 

 

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()

    def __unicode__(self):
        return self.name

 

 

 

这样重新启动,输入下面命令,就可以分辨出来。

 

>>> from books.models import Publisher

 

>>> publisher_list = Publisher.objects.all()

 

>>> publisher_list

 

[<Publisher: Apress>, <Publisher: O'Reilly>]

 


(2)数据库更新

 


例子:

 

>>> p = Publisher(name='Apress',

 

...     address='2855 Telegraph Ave.',

 

...      city='Berkeley',

 

...      state_province='CA',

 

...      country='U.S.A.',

 

...         website='http://www.apress.com/')

 

>>> p.save()

 

>>> p

 

<Publisher: Apress>

 

>>> p.id

 

3

 

>>> p.name = 'Apress Publishing'

 

>>> p.save()

 

>>> p

 

<Publisher: Apress Publishing>

 

 

 

注意:下面这样是更行不了的

 

>>> Publisher.objects.all()[0].name='AAAAAA'

 

>>> Publisher.objects.all()[0].save()

 

>>> Publisher.objects.all()[0]

 

<Publisher: Apress Publishing>

 

 

 

得要这样更新

 

>>> p = Publisher.objects.get(name='Apress')

 

>>> p

 

<Publisher: Apress>

 

>>> p.name = 'Apress Publishing'

 

>>> p.save()

 

>>> p

 

<Publisher: Apress Publishing>

 

 

 

上面的更行方法,用l了save(),这样不管有没有改过的数据,都会更行。可以用update(...),它只会更新要改的

 

>>> Publisher.objects.filter(id=1).update(name='Apress')

 

1

 

>>> Publisher.objects.all()

 

[<Publisher: Apress>, <Publisher: O'Reilly>]

 

 

 

但是update(),对结果集(QuerySet)有效,get(),[0],无效

 

如下面的命令会报错

 

>>> Publisher.objects.get(id=1).update(name='Apress')

 

Traceback (most recent call last):

 

  File "<console>", line 1, in <module>

 

AttributeError: 'Publisher' object has no attribute 'update'

 

 

(3)选择对象

 

 

Publisher.objects.all()显示所有对象

 

>>> Publisher.objects.all()

 

[<Publisher: Apress>, <Publisher: O'Reilly>]

 

Publisher.objects.filter(name='Apress')

 


 

Publisher.objects.filter(...) 筛选

 

>>> Publisher.objects.filter(name='Apress')

 

[<Publisher: Apress>]

 


 

filter(...) 可以有多个参数,相当与SQL中的AND

 

>>> Publisher.objects.filter(country="U.S.A.",state_province="CA")

 

[<Publisher: Apress>]

 


 

如果想使用SQL中的 LIKE 查询,要用 XX__contains

 

>>> Publisher.objects.filter(name__contains="press")

 

[<Publisher: Apress>]

 

name__contains="press" 相当与  LIKE “%press%”

 


(4)获取单个对象

 


filter 只要满足条件的都会输出

 

获取单个对象用get

 

>>> Publisher.objects.get(name='Apress')

 

<Publisher: Apress>

 


 

如果满足的不止一个会有异常,如果没有会抛出DoesNotExist异常

 

>>> Publisher.objects.get(country='U.S.A.')

 

Traceback (most recent call last):

 

  File "<console>", line 1, in <module>

 

  File "/usr/lib64/python2.7/site-packages/django/db/models/manager.py", line 151, in get

 

    return self.get_queryset().get(*args, **kwargs)

 

  File "/usr/lib64/python2.7/site-packages/django/db/models/query.py", line 310, in get

 

    (self.model._meta.object_name, num))

 

MultipleObjectsReturned: get() returned more than one Publisher -- it returned 2!

 

 

 


(5)数据库排序


 

order_by

 

>>> Publisher.objects.order_by("name")

 

[<Publisher: Apress>, <Publisher: O'Reilly>]

 


 

倒叙,只需要,加上“-”

 

>>> Publisher.objects.order_by("-name")

 

[<Publisher: O'Reilly>, <Publisher: Apress>]

 


(6)连锁查询

 


例子:

 

>>> Publisher.objects.filter(country="U.S.A.").order_by("-name")

 

[<Publisher: O'Reilly>, <Publisher: Apress>]

 


(7)限制返回查询

 


例子:

 

>>> Publisher.objects.order_by("-name")[0]

 

<Publisher: O'Reilly>

 

>>> Publisher.objects.order_by("-name")[0:2]

 

[<Publisher: O'Reilly>, <Publisher: Apress>]

 


(8)删除对象

 

用 delete()

 

>>> Publisher.objects.all()

 

[<Publisher: Apress>, <Publisher: O'Reilly>]

 

>>> Publisher.objects.filter(name='Apress').delete()

 

>>> Publisher.objects.all()

 

[<Publisher: O'Reilly>]

 

 

 

删除所有对象

 

>>> Publisher.objects.all().delete()

 

>>> Publisher.objects.all()

 

[]

 

 






  • liangchao

    评论: 非常明确

    2016-03-27 21:46:10          回复