疯狂暑期学习 Django学习笔记（三）—— 型号 model
參考：《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，假设用sqlite。要写完整路径
'USER': '', # 假设用sqlite，这个不用写
'PASSWORD': '', # 假设用sqlite，这个不用写
'HOST': '', # 告诉Django连接那一台. Not used with sqlite3. 假设用sqlite也空白
'PORT': '', # 设置port。空白就是默认，一般用默认的即可了。对于sqlite没用。
}
}'ENGINE' 能够有：
'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，就要安装相应DBMS的适配器。SQLite的，python默认已经装好了。
可用以下来命令測试数据库配置，假设没有显示错误信息。配置就是正确的。
>>> from django.db import connection
>>> cursor = connection.cursor()
2.创建APP
project跟APP的差别：一个是配置。一个是代码。
一个project能够包括非常多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。
前面你能够创建app。可是假设要用模型，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，内容例如以下
books/
├── admin.py
├── __init__.py
├── models.py
├── tests.py
└── views.py
然后在settings.py中INSTALLED_APPS中加入 'books'。
3.定义模型，模型安装
样例：
在models.py 中加入
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不论什么主键。除非指明，Django会自己主动为每一个模型生成一个自增长的单独主键 id
能够用以下的命令验证模型的有效性
python manage.py validate
能够用以下命令生成SQL语句。它这仅仅是生成SQL语句。不会运行
python manage.py sqlall books
假设想运行。运行以下语句（这个语句，在里加入新的模型或者app时才实用，改动删除模型syncdb不会做出不论什么反应）
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。必需要p1.save() 后才会真正生效
假设想一次性完毕插入运行以下的命令
>>> 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，在模板类中加入__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
这样又一次启动，输入以下命令，就能够分辨出来。
>>> from books.models import Publisher
>>> publisher_list = Publisher.objects.all()
>>> publisher_list
[<Publisher: Apress>, <Publisher: O'Reilly>]
（2）数据库更新
样例：
>>> 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：以下这样是更行不了的
>>> 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()。这样无论有没有改过的数据。都会更行。能够用update(...)，它仅仅会更新要改的
>>> Publisher.objects.filter(id=1).update(name='Apress')
1
>>> Publisher.objects.all()
[<Publisher: Apress>, <Publisher: O'Reilly>]
可是update(),对结果集（QuerySet）有效，get()，[0]。无效
如以下的命令会报错
>>> 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()显示全部对象
>>> 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(...) 能够有多个參数。相当与SQL中的AND
>>> Publisher.objects.filter(country="U.S.A.",state_province="CA")
[<Publisher: Apress>]
假设想使用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 仅仅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>
假设满足的不止一个会有异常，假设没有会抛出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
用order_by
>>> Publisher.objects.order_by("name")
[<Publisher: Apress>, <Publisher: O'Reilly>]
倒叙，仅仅须要，加上“-”
>>> Publisher.objects.order_by("-name")
[<Publisher: O'Reilly>, <Publisher: Apress>]
（6）连锁查询
样例：
>>> Publisher.objects.filter(country="U.S.A.").order_by("-name")
[<Publisher: O'Reilly>, <Publisher: Apress>]
（7）限制返回查询
样例：
>>> 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>]
删除全部对象
>>> Publisher.objects.all().delete()
>>> Publisher.objects.all()
[]
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