frist Django app— 二、 Model和管理界面

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Django是符合MVC架构的，这里现学习M—Model，而且Django自带了一个管理model（数据库）的界面，所以一并学习。

Database 配置

编辑Django的配置文件settings.py进行配置

添加polls app，修改后如下

INSTALLED_APPS = [
'django.contrib.admin',# 管理界面
'django.contrib.auth', # 认证系统
'django.contrib.contenttypes',# 框架的content type
'django.contrib.sessions', # session framework
'django.contrib.messages', # messages framework
'django.contrib.staticfiles', # 管理静态文件的framework
'polls.apps.PollsConfig', # 我们自己的app
]

最后一行位新添加的，表示新增一个app，类polls.apps.PoolsConfig定义了app，名称为“polls”（可以打开这个类看到）。

还可以看到很多其他的app，我们之前说过，一个project可以有多个app，一个app可以属于多个project，这个的实现方式就是这样，每个app都位于不同的包下面，如果一个project想包含一个app，只需要把这个app的包的配置写在这儿就可以了。

接下来配置数据库，修改完之后如下

DATABASES = {
'default': {
'ENGINE': 'django.db.backends.sqlite3',
'NAME': 'polls.db',
}
}

Django支持大多数主流的数据库，包括postgresql，mysql，sqlite等，这里为了简单就直接用sqlite，如果使用mysql应该配置成如下（其他类似）

DATABASES = {
'default': {
'ENGINE': 'django.db.backends.mysql',
'NAME': 'django',
'USER': 'root',
'PASSWORD': 'root',
'HOST': 'localhost',
'PORT': '',
}
}

数据库至此配置完成，接下来就是创建model

创建model

编辑mysite/polls/models.py

from __future__ import unicode_literalsfrom django.db import models# Create your models here.
class Question(models.Model):
# CharField：字段是字符串类型，有一个必要参数——字符串长度
question_text = models.CharField(max_length=200)
# DateField：字段是日期类型
publ_date = models.DateField('date published')    def __unicode__(self):
        return self.question_textclass Choice(models.Model):
# question作为choice的外键，这里是多对一关系，删除的时候进行级联，Django还支持：many-to-one, many-to-many, and one-to-one.
question = models.ForeignKey(Question, on_delete=models.CASCADE)
choice_text = models.CharField(max_length=200)
votes = models.IntegerField(default=0)    def __unicode__(self):
        return self.choice_text

每个model继承自models.Model,会继承一些常用的操作方法。每个class对应的属性都对应数据库中表中的字段——这也就是ORM

生成数据库表结构

# 告诉Django model改变了，并且保存为一个migration
python manage.py makemigrations

运行该命令，输出如下内容，并在pools/migrations下生成0001_initial.py

Migrations for 'polls':
0001_initial.py:
- Create model Choice
- Create model Question
- Add field question to choice

我们可以看看Django根据这个migration会怎么生成表结构运行

# 0001 为之前生成的0001_initial.py的前缀，表示第一个版本的migration
python manage.py sqlmigrate polls 0001

输出

BEGIN;
--
-- Create model Choice
--
CREATE TABLE "polls_choice" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "choice_text" varchar(200) NOT NULL, "votes" integer NOT NULL);
--
-- Create model Question
--
CREATE TABLE "polls_question" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "question_test" varchar(200) NOT NULL, "publ_date" date NOT NULL);
--
-- Add field question to choice
--
ALTER TABLE "polls_choice" RENAME TO "polls_choice__old";
CREATE TABLE "polls_choice" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "choice_text" varchar(200) NOT NULL, "votes" integer NOT NULL, "question_id" integer NOT NULL REFERENCES "polls_question" ("id"));
INSERT INTO "polls_choice" ("choice_text", "votes", "id", "question_id") SELECT "choice_text", "votes", "id", NULL FROM "polls_choice__old";
DROP TABLE "polls_choice__old";
CREATE INDEX "polls_choice_7aa0f6ee" ON "polls_choice" ("question_id");COMMIT;

Django会运行上面这些语句来生成数据库表结构，我们可以看到生成两张表分别对应两个model，给question这张表添加一个外键。

现在我们可以生成数据库表结构了，这个命令就是将上面生成的migration应用到数据库

python manage.py migrate

输出

Operations to perform:
Apply all migrations: admin, contenttypes, polls, auth, sessions
Running migrations:
Rendering model states... DONE
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying admin.0002_logentry_remove_auto_add... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying auth.0007_alter_validators_add_error_messages... OK
Applying polls.0001_initial... OK
Applying sessions.0001_initial... OK

到这儿，数据库表结构生成完毕，我们可以使用sqlite3查看生成的表结构

sqlite3 polls.db
#以下为输出内容
SQLite version 3.8.7.1 2014-10-29 13:59:56
Enter ".help" for usage hints.
sqlite> .tables
auth_group django_admin_log
auth_group_permissions django_content_type
auth_permission django_migrations
auth_user django_session
auth_user_groups polls_choice
auth_user_user_permissions polls_question

使用API操作model

# 这里用的是ipython，进入django命令行
python manage.py shell
Python 2.7.9 (default, Mar 1 2015, 18:22:53)
Type "copyright", "credits" or "license" for more information.IPython 2.3.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
# 导入model
In [2]: from polls.models import Choice, Question
# 查看所有的question对象
In [3]: Question.objects.all()
Out[3]: [<Question: what`s up?>]
# 获取id为0的对象，没有id为0的对象，所以会报错
In [5]: Question.objects.get(id=0)
---------------------------------------------------------------------------
DoesNotExist Traceback (most recent call last)
<ipython-input-5-bd4c3a1273f2> in <module>()
----> 1 Question.objects.get(id=0)/usr/local/lib/python2.7/dist-packages/Django-1.9.7-py2.7.egg/django/db/models/manager.pyc in manager_method(self, *args, **kwargs)
120 def create_method(name, method):
121 def manager_method(self, *args, **kwargs):
--> 122 return getattr(self.get_queryset(), name)(*args, **kwargs)
123 manager_method.__name__ = method.__name__
124 manager_method.__doc__ = method.__doc__/usr/local/lib/python2.7/dist-packages/Django-1.9.7-py2.7.egg/django/db/models/query.pyc in get(self, *args, **kwargs)
385 raise self.model.DoesNotExist(
386 "%s matching query does not exist." %
--> 387 self.model._meta.object_name
388 )
389 raise self.model.MultipleObjectsReturned(DoesNotExist: Question matching query does not exist.
# 获取id为1的对象
In [6]: Question.objects.get(id=1)
Out[6]: <Question: what`s up?>In [7]: q = Question.objects.get(id=1)
# 删除该对象
In [8]: q.delete()
Out[8]: (4, {u'polls.Choice': 3, u'polls.Question': 1})
# 查看发现已经删除
In [9]: Question.objects.all()
Out[9]: []In [11]: from django.utils import timezone
# 新建一个对象
In [13]: q = Question(question_text="What's new?", publ_date=timezone.now())
# 保存到数据库
In [15]: q.save()
# 保存到数据库之后Django自动生成了id，只有在save之后才有
In [16]: q.id
Out[16]: 2
# 查看字段值
In [17]: q.question_text
Out[17]: "What's new?" In [18]: q.publ_date
Out[18]: datetime.datetime(2016, 7, 10, 13, 12, 40, 146050, tzinfo=<UTC>)In [19]: q.question_text = "What's up?"In [20]: q.save()In [22]: q
Out[22]: <Question: What's up?>In [23]: Question.objects.all()
Out[23]: [<Question: What's up?>]In [24]: Question.objects.filter(id=1)
Out[24]: []
# 使用filter查询
In [25]: Question.objects.filter(id=2)
Out[25]: [<Question: What's up?>]In [26]: Question.objects.filter(question_text__startswith='What')
Out[26]: [<Question: What's up?>]In [29]: Question.objects.get(publ_date__year=timezone.now().year)
Out[29]: <Question: What's up?>
# 查看question关联的choice
In [30]: q.choice_set.all()
Out[30]: []
# 新建一个choice关联到question
In [31]: q.choice_set.create(choice_text='Not much', votes=0)
Out[31]: <Choice: Not much>In [32]: q.choice_set.create(choice_text='The sky', votes=0)
Out[32]: <Choice: The sky>In [33]: c = q.choice_set.create(choice_text='Just hacking again', votes=0)
# 查看choice对应的question
In [34]: c.question
Out[34]: <Question: What's up?>In [35]: q.choice_set.all()
Out[35]: [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]In [36]: q.choice_set.count()
Out[36]: 3

Django提供了很多API来操作model，包括新建、更新、删除、关联、从一个对象查询关联的对象等等，除此之外Django还提供了web界面对model进行管理。

Django Admin

使用以下命令依次输入用户名、邮箱（注意邮箱）、密码（8位以上的字母数字组成）

python manage.py createsuperuser

访问http://127.0.0.1:8000/admin/登陆，可以看到管理界面，但是现在并没有mode，接下来注册model

编辑polls/admin.py

from django.contrib import admin
from polls.models import Choice, Question# Register your models here.
admin.site.register(Choice)
admin.site.register(Question)

再次登陆就可以看到model：Choice，Question，可以在界面上增删改查，so easy