Django 框架中模型的使用

创建模型

polls/models.py

from django.db import models

class Question(models.Model):
    question_text = models.CharField(u'问题内容', max_length=200, null=False, default='')
    pub_date = models.DateTimeField(u'时间')

class Choice(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE, verbose_name="问题ID")
    choice_text = models.CharField(u'选项内容', max_length=200, null=False, default='')
    votes = models.PositiveIntegerField(u'投票数量', null=False, default=0)

激活模型

在项目配置文件中添加应用：

# mysite/settings.py

INSTALLED_APPS = [
    'polls.apps.PollsConfig',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

生成迁移文件：

> py manage.py makemigrations polls

查看迁移文件的内容：

> py manage.py sqlmigrate polls 0001

运行迁移：

> py manage.py migrate

测试模型 API

> py manage.py shell

>>> from polls.models import Choice, Question

>>> Question.objects.all()
<QuerySet []>

>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())
>>> q.save()
>>> q.id
1
>>> q.question_text
"What's new?"
>>> q.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)

>>> q.question_text = "What's up?"
>>> q.save()

>>> Question.objects.all()
<QuerySet [<Question: Question object (1)>]>

编辑 Question 模型的代码改变对象的输出内容：

# polls/models.py

import datetime

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

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

class Choice(models.Model):
    # ...
    def __str__(self):
        return self.choice_text

重新打开交互式命令行：

> py manage.py shell

>>> from polls.models import Choice, Question

>>> Question.objects.all()
<QuerySet [<Question: What's up?>]>

>>> Question.objects.filter(id=1)
<QuerySet [<Question: What's up?>]>

>>> Question.objects.filter(question_text__startswith='What')
<QuerySet [<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?>

# 查询不存在的ID会抛出异常
>>> Question.objects.get(id=2)
DoesNotExist: Question matching query does not exist.

# 通过主键查询
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True

# 关联查询问题的选项
>>> q.choice_set.all()
<QuerySet []>

# 创建选项数据
>>> 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?>

# 关联查询问题的选项
>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> q.choice_set.count()
3

>>> Choice.objects.filter(question__pub_date__year=current_year)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>

>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()