Django 1.7 初级教程or学习笔记（二）

本文链接：https://blog.youkuaiyun.com/u010738165/article/details/39735517

Django 可以工作之后，我们开始新建app。

A project can containmultiple apps. An app can be in multiple projects.

进入 mysite/ ，现在在与 manage.py 同级目录中（简单说，就是和manage.py在同一个文件夹。。。）

执行命令：

  python manage.py startapp polls

命令成功执行之后，可以看见 polls 结构如下：

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

在polls app 中，创建两个模块 Question 和 Choice , Question 中包含 “question” 和 ‘date’ ,Choice 中包含 “ choice” 和 “tally”(投票计数)，并且 Question 是Choice 的外键。

编辑 polls/models.py 文件，代码如下：

 import datetime

 from django.db import models
 from django.utils import timezone
 class Question(models.Model):

    question_text = models.CharField(max_length=200)

    pub_date = models.DateTimeField('date published')
     def __unicode__(self):              
        return self.question_text
 class Choice(models.Model):

        question = models.ForeignKey(Question)

        choice_text = models.CharField(max_length=200)

        votes = models.IntegerField(default=0)

     def was_published_recently(self):
         return self.pub_date >= timezone.now() - datetime.timedelta(days=1)

     def __unicode__(self):                       
         return self.choice_text

模块编辑好了之后，激活模块，进行下面三步：

1.告诉项目，现在多了一个名为“polls” 的app。

在 mysite/settings.py 中，修改以下部分：

  INSTALLED_APPS = (
     'django.contrib.admin',
     'django.contrib.auth',
     'django.contrib.contenttypes',
     'django.contrib.sessions',
     'django.contrib.messages',
     'django.contrib.staticfiles',
     'polls',  #只是增加了这一点
 )

现在，项目 mysite 已经知道多了一个名为"polls" 的 app 了。

2.我们还要告诉它， "polls" 的一些具体的情况，比如说， polls 中存在两个模块。

执行以下命令：

  python manage.py makemigrations polls

有以下输出则代表项目已经接受了 polls 的具体情况：

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

3. 增加了一个 app，就要创建相应的表（或者其他改变），用命令去执行相应的改变。

  python manage.py sqlmigrate polls 0001

出现类似以下的输出，则表示成功了：（不一定会一模一样）

BEGIN;
CREATE TABLE polls_question (
    "id" serial NOT NULL PRIMARY KEY,
    "question_text" varchar(200) NOT NULL,
    "pub_date" timestamp with time zone NOT NULL
);

CREATE TABLE polls_choice (
    "id" serial NOT NULL PRIMARY KEY,
    "question_id" integer NOT NULL,
    "choice_text" varchar(200) NOT NULL,
    "votes" integer NOT NULL
);

CREATE INDEX polls_choice_7aa0f6ee ON "polls_choice" ("question_id");

ALTER TABLE "polls_choice"
  ADD CONSTRAINT polls_choice_question_id_246c99a640fbbd72_fk_polls_question_id
    FOREIGN KEY ("question_id")
    REFERENCES "polls_question" ("id")
    DEFERRABLE INITIALLY DEFERRED;
COMMIT;

4.我们知道了有这些改动，然后接下来，告诉数据库，有这样的变动。

命令：

  python manage.py migrate

输出：（可能只会输出一部分，我觉得只要有最后那句 “Applying polls.0001_initial... OK”，就可以认为成功了）

 Operations to perform:
   Synchronize unmigrated apps: sessions, admin, messages, auth, staticfiles, contenttypes
   Apply all migrations: polls
 Synchronizing apps without migrations:
   Creating tables...
   Installing custom SQL...
   Installing indexes...
 Installed 0 object(s) from 0 fixture(s)
 Running migrations:
   Applying polls.0001_initial... OK

现在 app 已经创建好并且和安装到项目之中了，接下来测试一下。

计进入 Python shell 交互环境。

命令：

  python manage.py shell

出现 “>>>” 开始测试：

>>> from polls.models import Question, Choice>>> Question.objects.all()
[]
>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())>>> q.save()>>> q.id1>>> q.question_text"What's new?">>> q.pub_datedatetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)>>> q.question_text = "What's up?">>> q.save()>>> Question.objects.all()[<Question: Question object>]

>>> from polls.models import Question, Choice
>>> Question.objects.all()
[<Question: What's up?>]
>>> Question.objects.filter(id=1)
[<Question: What's up?>]
>>> Question.objects.filter(question_text__startswith='What')
[<Question: What's up?>]
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Question.objects.get(pub_date__year=current_year)
<Question: What's up?>
>>> Question.objects.get(pk=1)
<Question: What's up?>
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True
>>> q = Question.objects.get(pk=1)
>>> 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)
>>> c.question
<Question: What's up?>
>>> q.choice_set.all()
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> q.choice_set.count()
3
>>> Choice.objects.filter(question__pub_date__year=current_year)
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()
源代码：
https://github.com/Alkaid-seven/Django1.7_example_code