models.py相关API-优快云博客

本文介绍如何使用 Django 创建一个投票应用，包括模型定义、数据操作及查询。演示了 Question 和 Choice 模型的创建过程，以及通过 Python shell 进行数据增删改查的具体方法。

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)

    question_text = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')


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

python shell

from polls.models import Choice, Question
from django.utils import timezone

q = Question(question_text="What's new?", pub_date=timezone.now())
q.save()

q.id #输出：1
q.question_text #输出：What's new?
q.pub_date #输出：datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)

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

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

Question.objects.get(pub_date__year = timezone.now().year) #输出：<Question: What's up?>
Question.objects.get(id=2)   #输出：报错，因为只有1条记录
Question.objects.get(pk=1)   #输出：<Question: What's up?>
q = Question.objects.get(pk=1)
q.was_published_recently()   #输出：True

q = Question.objects.get(pk=1)
q.choice_set.all()  #输出：<QuerySet []>

q.choice_set.create(choice_text='Not much', votes=0)  #输出：<Choice: Not much>
q.choice_set.create(choice_text='The sky', votes=0)  #输出：<Choice: The sky>
c = q.choice_set.create(choice_text='Just hacking again', votes=0)
c.question   #输出：<Question: What's up?>
q.choice_set.all()
#输出：<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
q.choice_set.count() #输出：3


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

c = q.choice_set.filter(choice_text__startswith='Just hacking')
c.delete()  #删除该记录