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Django学习笔记(三)模型model

作者:  发布日期:2014-07-08 20:08:42
Tag标签:模型  笔记  
  • 疯狂的暑假学习之 Django学习笔记(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

    用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()

    []



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