Django笔记：6.玩转API

玩转API

现在，让我们进入Python的交互式shell，玩转这些Django提供给你的API。在cmd中使用如下命令来调用Python shell：

python manage.py shell

一旦你进入这个shell，请探索这些数据库 API：

In [1]: from polls.models import Question, Choice

# Question暂时没有内容
In [2]: Question.objects.all()
Out[2]: []

# django的时间模块，用timezone.now()可返回当前时间
In [3]: from django.utils import timezone

In [4]: timezone.now()
Out[4]: datetime.datetime(2016, 5, 11, 13, 4, 38, 930525, tzinfo=<UTC>)

# 填写Question的question_text和pub_date两项内容
In [5]: q = Question(question_text="What's new?", pub_date=timezone.now())

# 保存
In [6]: q.save()

# 返回ID
In [7]: q.id
Out[7]: 1

# 返回Question里面的question_text字段的值
In [8]: q.question_text
Out[8]: "What's new?"

# 返回Question里面的pub_date字段的内容
In [9]: q.pub_date
Out[9]: datetime.datetime(2016, 5, 10, 2, 54, 11, 312500, tzinfo=<UTC>)

# 改变question_text的内容并保存
In [10]: q.question_text = "What's up?"
In [11]: q.save()

# 可见，question_text的内容改变了
In [12]: q.question_text
Out[12]: "What's up?"

# 返回数据库中所有的Question对象
In [13]: Question.objects.all()
Out[13]: [<Question: Question object>]

先等一下。<Question: Question object>对于这个对象是一个完全没有意义的表示。让我们来修复这个问题，编辑Question模型（在polls/models.py文件中）并添加一个__str__()方法给Question和Choice：

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

给你的模型添加__str__()方法很重要，不仅会使你自己在使用交互式命令行时看得更加方便，而且会在Django自动生成的管理界面中使用对象的这种表示。

然后为Question添加一个自定义的方法：

import datetime

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


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

现在，你的代码是这样的：

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

# Create your models here.

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

    def __str__(self):              # __unicode__ on Python 2
        return self.question_text

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



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

    def __str__(self):              # __unicode__ on Python 2
        return self.choice_text

保存这些改动，然后通过python manage.py shell再次打开一个新的Python 交互式shell：

In [1]: from polls.models import Question,Choice

# 添加__str__()方法后可以显示Question的内容了
In [2]: Question.objects.all()
Out[2]: [<Question: What's up?>]

# Django提供的数据库查询功能
# filter()用来筛选指定参数
In [3]: Question.objects.filter(id=1)
Out[3]: [<Question: What's up?>]

# 查询以'What'开头的记录
In [4]: Question.objects.filter(question_text__startswith='What')
Out[4]: [<Question: What's up?>]

# 查询pub_date值为本年的记录
In [5]: from django.utils import timezone
In [6]: current_year = timezone.now().year
In [7]: Question.objects.get(pub_date__year=current_year)
Out[7]: <Question: What's up?>

# 查询一个不存在的健会报错
In [8]: Question.objects.get(id=2)
---------------------------------------------------------------------------
DoesNotExist                              Traceback (most recent call last)
<ipython-input-8-e5ad49b3e3e3> in <module>()
----> 1 Question.objects.get(id=2)

…………

DoesNotExist: Question matching query does not exist.

# 通过主键(primary-key)查询
In [9]: Question.objects.get(pk=1)
Out[9]: <Question: What's up?>

# 获取主键（这里是ID）为1的记录
In [10]: q = Question.objects.get(pk=1)

In [11]: q
Out[11]: <Question: What's up?>

# 执行自定义的was_published_recently方法
In [12]: q.was_published_recently()
Out[12]: True

# 返回choice_set，现在没有内容
In [13]: q.choice_set.all()
Out[13]: []

# 写入三个choices
In [14]: q.choice_set.create(choice_text='Not much', votes=0)
Out[14]: <Choice: Not much>

In [15]: q.choice_set.create(choice_text='The sky', votes=0)
Out[15]: <Choice: The sky>

In [16]: c = q.choice_set.create(choice_text='Just hacking again', votes=0)

# Choice对象有一个API通道和Question对象关联，在这里question是Choice的外键
In [17]:  c.question
Out[17]: <Question: What's up?>

# 反过来，也可以通过Question对象来访问Choice对象
In [18]: q.choice_set.all()
Out[18]: [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]

# count()方法可以取得选项数量。
In [19]: q.choice_set.count()
Out[19]: 3

# 可以透过API查询关联的表，用双下划线分割它们
In [20]: Choice.objects.filter(question__pub_date__year=current_year)
Out[20]: [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]

In [21]: c = q.choice_set.filter(choice_text__startswith='Just hacking')

In [22]: c.delete()
Out[22]: (1, {'polls.Choice': 1})

更多关于模型关联的信息，请查看访问关联的对象。更多关于如何在这些API中使用双下划线来执行字段查询的信息，请查看字段查询。更多关于数据库API的信息，请查看我们的数据库API参考。