Django入门笔记【一】

入门笔记翻译整理自：https://docs.djangoproject.com/en/1.8/

*该笔记将使用一个关于投票网络应用（poll application）的例子来阐述Django的用法。

1. 查看Django是否安装及版本

 $ python -c "import django; print(django.get_version())" 

2. 创建一个项目（project）

通过cd方式进入自创目录，然后运行：

 $ django-admin startproject mysite 

这将创建一个名为mysite的项目：

mysite/
    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        wsgi.py

3. 数据库设置（database setup）

在数据库中创建表格：

 $ python manage.py migrate 

4. 开发服务器（development server）

进入mysite目录，并运行

 $ python manage.py runserver 

也可以指名地址和端口

 $ python manage.py runserver 0.0.0.0:8000 

5. 创建模型（models）

在manage.py所在文件夹中，创建投票网络应用

 $ python manage.py startapp polls 

文件夹结构如下：

polls/
    __init__.py
    admin.py
    migrations/
        __init__.py
    models.py
    tests.py
    views.py

编辑polls/models.py:

#polls/models.py

from django.db import models

class Question(models.Model):
    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    question = models.ForeignKey(Question)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

6. 激活模型

Django应用是可插拔的（pluggable），在mysite/settings.py中插入polls应用

#mysite/settings.py

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'polls',
)

然后运行代码

$ python manage.py makemigrations polls

这会创建文件polls/migrations/0001_initial.py

然后运行代码

$ python manage.py sqlmigrate polls 0001

这会显示（但并不创建）Django认为polls所需要的数据库表格

运行代码

$ python manage.py migrate

这会创建polls所需要的数据库表格。

7. 使用API

使用manage.py初始化python

$ python manage.py shell

进入python shell，就可以开始探索数据库API

>>> from polls.models import Question, Choice

# No questions are in the system yet
>>> Question.objects.all()
[]

# Create a new Question
>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())

# Save the object into database
>>> q.save()

# The object has an ID
>>> q.id
1

# Access model field values via Python attributes
>>> q.question_text
"What's new?"
>>> q.pub_date
datetime.datetime(2012, 2, 26,13, 0, 0, 775217, tzinfo=<UTC>)

# Change values by changing the attributes
>>> q.question_text = "What's up?"
>>> q.save()

# object.all() displays all the questions in the database
>>> Question.objects.all()
[<Question: Question object>]

无疑，最后的返回值<Question: Question object>不包含任何信息量。尝试对Question和Choice加入__str__()方法来改进：

# polls/models.py
from django.db import models

class Question(models.Model):
    # ...
    def __str__(self):        #__unicode__ on Python 2
        return self.question_text

class Choice(models.Model):
    # ...
    def __str__(self):        #__unicode__ on Python 2
        return self.choice_text

__str__()和__unicode__()都是Python自带方法，我们可以自定义一个方法：

# polls/models.py

import datetime

from django.db import models
from djangol.utils import timezone

class Question(models.Model):
    # ...
    def was_published_recently(self):
        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

将这些修改保存，并重新运行 python manage.py shell 

>>> from polls.models import Question, Choice 

# Make sure our __str__() addition worked.
>>> Question.objects.all()
[<Question: What's up?>]

# Django provides a rich database lookup API
>>> Question.objects.filter(id=1)
[<Question: What's up?>]
>>> Question.objects.filter(question_text__startswith='What')
[<Question: What's up?>]

# Get the question that published this year
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Question.objects.get(pub_date__year=current_year)
<Question: What's up?>

# Request an ID that doesn't exist, this will raise an exception
>>> Question.objects.get(id=2)

# Lookup by a primary key, identical to Question.objects.get(id=1)
>>> Question.objects.get(pk=1)
<Question: What's up?>

# Make sure our custom method worked
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True

为问题创建选项：

# Give the Question a couple of Choices. 
>>> q = Question.objects.get(pk=1)

# Display any choices from the related object set
>>> q.choice_set.all()
[]

# Create three choices
>>> q.choice_set.create(choice_text='Not much', votes=0)
<Choice: Not much>
>>> q.choice_set.create(choice_text='The sky', votes=0)
<Choice: The sky>
>>> c = q.choice_set.create(choice_text='Just hacking again', votes=0)

# Choice objects have API access to their related Question objects
>>> c.question
<Question: What's up?>

# And vice versa: Question objects get access to Choice objects
>>> q.choice_set.all()
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> q.choice_set.count()
3

# Use double underscores to separate relationships. 
>>> Choice.objects.filter(question__pub_date__year=current_year)
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]

# Delete one of the choices
>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()

--The end--