Django - “get raise self.model.DoesNotExist：课程匹配查询不存在

Question

我正在使用 Django 后端和 Vue.js 作为前端的教程构建 LMS。当我尝试对网站上的课程发表评论时，我不断收到以下回溯。

Traceback (most recent call last):
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/views/generic/base.py", line 69, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/rest_framework/decorators.py", line 50, in handler
    return func(*args, **kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/relate_django/course/views.py", line 74, in add_comment
    course = Course.objects.get(slug=course_slug)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/Users/markmckeon/Django_Stuff/Relate/environment_3_8_8/lib/python3.8/site-packages/django/db/models/query.py", line 439, in get
    raise self.model.DoesNotExist(
course.models.Course.DoesNotExist: Course matching query does not exist.
[23/Dec/2021 12:18:25] "POST /api/v1/courses/undefined/Heat_Transfer_understand/ HTTP/1.1" 500 102326

我相信 Django 抛出此错误是因为在 views.py 中的课程模型上使用了外键：

from django.shortcuts import render
from rest_framework import serializers
from django.core.exceptions import ObjectDoesNotExist

from rest_framework.response import Response
from rest_framework.decorators import api_view, authentication_classes, permission_classes

from .models import Course, Lesson, Comment, Category
from .serializers import CourseListSerializer, CourseDetailSerializer, LessonListSerializer, CommentsSerializer, CategorySerializer


@api_view(['GET'])
@authentication_classes([])
@permission_classes([])
def get_course(request, slug):
    
    course = Course.objects.get(slug=slug)
    course_serializer = CourseDetailSerializer(course)
    lesson_serializer = LessonListSerializer(course.lessons.all(), many=True)

    if request.user.is_authenticated:
        course_data = course_serializer.data
    else:
        course_data = {}
    data = {
        'course': course_data,
        'lessons': lesson_serializer.data
    }

                        
    return Response(data)

@api_view(['GET'])
def get_comments(request, course_slug, lesson_slug):
    lesson = Lesson.objects.get(slug=lesson_slug)
    serializer = CommentsSerializer(lesson.comments.all(), many=True)
    return Response(serializer.data)

@api_view(['POST'])
def add_comment(request, course_slug, lesson_slug):
    data = request.data
    name = data.get('name')
    content = data.get('content')

    course = Course.objects.get(slug=course_slug)
    lesson = Lesson.objects.get(slug=lesson_slug)

    comment = Comment.objects.create(course=course, lesson=lesson, name=name, content=content, created_by=request.user)

    serializer = CommentsSerializer(comment)

    return Response(serializer.data)

由于这个错误，它也没有动态更新我课程中的课程标题。 我研究过当 Django 无法生成唯一名称时，Django 会使用外键抛出这些异常？ 任何有关我如何实现 try 和 except 块的指导都会非常有帮助。

这里是models.py：

from django.conf import settings
from django.contrib.auth.models import User
from django.db import models

class Category(models.Model):
    title = models.CharField(max_length=255)
    slug = models.SlugField()
    short_description = models.TextField(blank=True, null=True)
    created_at = models.DateField(auto_now_add=True)

    class Meta:
        verbose_name_plural = 'Categories'

    def __str__(self):
        return self.title

class Course(models.Model):
    categories = models.ManyToManyField(Category)
    title = models.CharField(max_length=255)
    slug = models.SlugField()
    short_description = models.TextField(blank=True, null=True)
    long_description = models.TextField(blank=True, null=True)
    created_at = models.DateField(auto_now_add=True)
    image = models.ImageField(upload_to='uploads', blank=True, null=True)

    def __str__(self):
        return self.title

    def get_image(self):
        if self.image:
            return settings.WEBSITE_URL + self.image.url
        else:
            return 'http://bulma.io/images/placeholders/1280x960.png'

class Lesson(models.Model):
    DRAFT = 'draft'
    PUBLISHED = 'published'

    CHOICES_STATUS = (
        (DRAFT, 'Draft'),
        (PUBLISHED, 'Published')
    )

    ARTICLE = 'article'
    QUIZ = 'quiz'

    CHOICES_LESSON_TYPE = (
        (ARTICLE, 'Article'),
        (QUIZ, 'Quiz')
    )

    course = models.ForeignKey(Course, related_name='lessons', on_delete=models.CASCADE)
    title = models.CharField(max_length=255)
    slug = models.SlugField()
    short_description = models.TextField(blank=True, null=True)
    long_description = models.TextField(blank=True, null=True)
    status = models.CharField(max_length=20, choices=CHOICES_STATUS, default=PUBLISHED)
    lesson_type = models.CharField(max_length=20, choices=CHOICES_LESSON_TYPE, default=ARTICLE)

class Comment(models.Model):
    course = models.ForeignKey(Course, related_name='comments', on_delete=models.CASCADE)
    lesson = models.ForeignKey(Lesson, related_name='comments', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    created_by = models.ForeignKey(User, related_name='comments', on_delete=models.CASCADE)

Answer 1

问题已解决。

我有 user.is_authenticated 有条件地阻止了 views.py 中的 course_data 字典。

哦。浪费了很多时间。但是我学到了东西！