+ Django tutorial 4- actual hands-entry Pycharm first test API

Disclaimer: This article is a blogger original article, shall not be reproduced without the bloggers allowed. https://blog.csdn.net/baidu_39459954/article/details/90241261

Objects created Question

Now let's get into the interactive Python command line, try a variety of API Django created for you. Open Python commands using the following command line:
Python manage.py shell
or we can open Pycharm of Tool-> Python Console
Python 3.7.3 (v3.7.3: ef4ec6ed12, Mar 25 2019, 22:22:05) [the MSC v.1916 'bit 64 (the AMD64)] ON Win32
the Django 2.2.1

Choice and Question introduced model classes we created last article:

>>> from polls.models import Choice, Question

Question of the query, is now empty:

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

Create a new Question, recommended timezone.now () instead datetime.datetime.now in Django (), so the introduction timezone:

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

Use save (), save Question into the database just created:

>>> q.save()

Query the database can be seen, the data has been saved:

Question query object created

ID is automatically generated, q.id can query the current id number:

>>> q.id
1

通过python属性访问模型字段值：
Access model field values via Python attributes.

>>> q.question_text
"What's new?"
>>> q.pub_date
datetime.datetime(2019, 5, 19, 16, 23, 13, 320097)

通过修改属性修改对应的值，然后再调用save():

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

objects.all()显示数据库中所有的对象：

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

__ str __() 方法

但是输出结果 <Question: Question object (1)> 对于我们了解这个对象的细节没什么帮助。我们可以通过编辑 Question 模型的代码（位于 polls/models.py 中）来修复这个问题。给 Question 和 Choice 增加 __str __() 方法。

from django.db import models


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

    def __str__(self):
        return self.question_text


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

    def __str__(self):
        return self.choice_text

重新打开Python Console，再次查询，确认我们加的__str __() 生效了：

>>> from polls.models import Choice, Question
>>> Question.objects.all()
<QuerySet [<Question: What's up?>]>

数据库查找API

Django提供了丰富的数据库查找API，它完全由关键字参数驱动。

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

获取今年发布的问题：

>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Question.objects.get(pub_date__year=current_year)
<Question: What's up?>

如果请求不存在的ID，将引发异常：

>>> Question.objects.get(id=2)
Traceback (most recent call last):
    ...
polls.models.Question.DoesNotExist: Question matching query does not exist.

通过主键查找是最常见的情况，因此Django提供了主键精确查找的快捷方式，以下内容与Question.objects.get（id = 1）相同。

>>> Question.objects.get(pk=1)
<Question: What's up?>

自定义方法

给模型增加 __ str__() 方法是很重要的，这不仅仅能给你在命令行里使用带来方便，Django 自动生成的 admin 里也使用这个方法来表示对象。
注意：这些都是常规的 Python方法。让我们添加一个自定义的方法was_published_recently，这只是为了演示：

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 __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):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

    def __str__(self):
        return self.choice_text

重新连接，查看我们新加的自定义方法是否生效：

>>> from polls.models import Choice, Question 
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True

创建Choice对象

给提出的问题添加几个选择。
The create call constructs a new Choice object, does the INSERT statement, adds the choice to the set of available choices and returns the new Choice object. Django creates a set to hold the “other side” of a ForeignKey relation

(Eg selection problem) can be accessed via the API.

>>> q = Question.objects.get(pk=1)

Q display object (primary key 1) corresponding to the choice, currently empty.

>>> q.choice_set.all()
<QuerySet []>

Create three Choice:

>>> 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 object.

>>> c.question
<Question: What's up?>

And vice versa: Question Choice object can access the object.

>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> q.choice_set.count()
3

API will automatically track the relationship according to your needs, use double underscores to separate relationships, which can be as deep as you want multi-level; there is no limit.
Find pub_date select any problems at all this year (reusable created above us 'current_year' variable).

>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Choice.objects.filter(question__pub_date__year=current_year)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>

Use delete () delete a choice.

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

Query the database and found that the corresponding choice deleted

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