python - Django错误 "home.models.Friend.DoesNotExist: Friend matching query does not exist."

Question

我的项目运行良好，直到我不得不卸载并重新安装 MySQL 数据库并重新迁移/重新创建数据。

现在，当我导航到 /home/ 时，它会抛出此错误

DoesNotExist at /home/
Friend matching query does not exist. 

该查询确实存在于数据库中，并且所有其他页面都可以工作。

从命令行:

 Internal Server Error: /home/
    Traceback (most recent call last):
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
        response = get_response(request)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/core/handlers/base.py", line 126, in _get_response
        response = self.process_exception_by_middleware(e, request)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/core/handlers/base.py", line 124, in _get_response
        response = wrapped_callback(request, *callback_args, **callback_kwargs)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/views/generic/base.py", line 68, in view
        return self.dispatch(request, *args, **kwargs)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/views/generic/base.py", line 88, in dispatch
        return handler(request, *args, **kwargs)
      File "/Users/trillav/apps/max/home/views.py", line 16, in get
        friend = Friend.objects.get(current_user=request.user)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
        return getattr(self.get_queryset(), name)(*args, **kwargs)
      File "/Users/trillav/.virtualenvs/max/lib/python3.7/site-packages/django/db/models/query.py", line 399, in get
        self.model._meta.object_name
    home.models.Friend.DoesNotExist: Friend matching query does not exist.
    [31/Oct/2018 13:53:02] "GET /home/ HTTP/1.1" 500 81063

这是home.models:

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

class Post(models.Model):
    post = models.CharField(max_length=500)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)

class Friend(models.Model):
    users = models.ManyToManyField(User)
    current_user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='owner', null=True)

    @classmethod
    def make_friend(cls, current_user, new_friend):
        friend, created = cls.objects.get_or_create(
            current_user=current_user
        )
        friend.users.add(new_friend)

    @classmethod
    def lose_friend(cls, current_user, new_friend):
        friend, created = cls.objects.get_or_create(
            current_user=current_user
        )
        friend.users.remove(new_friend)

还有我的主页 View 功能:

from django.views.generic import TemplateView
from django.shortcuts import render, redirect
from django.contrib.auth.models import User

from home.forms import HomeForm
from home.models import Post, Friend

# Create your views here.
class HomeView(TemplateView):
    template_name = 'home/home.html'

    def get(self, request):
        form = HomeForm()
        posts = Post.objects.all().order_by('-created')
        users = User.objects.exclude(id=request.user.id)
        friend = Friend.objects.get(current_user=request.user)
        friends = friend.users.all()

        args = {
            'form': form, 'posts': posts, 'users': users, 'friends': friends
        }
        return render(request, self.template_name, args)

    def post(self, request):
        form = HomeForm(request.POST)
        if form.is_valid():
            post = form.save(commit=False)
            post.user = request.user
            post.save()
            text = form.cleaned_data['post']
        return redirect('home:home')

        args = {'form': form, 'text': text}
        return render(request, self.template_name, {'form': form})

def change_friends(request, operation, pk):
    friend = User.objects.get(pk=pk)
    if operation == 'add':
        Friend.make_friend(request.user, friend)
    elif operation == 'remove':
        Friend.lose_friend(request.user, friend)
    return redirect('home:home')

导致此错误的原因是什么？如何修复它？

Answer 1

views.py 中的第 16 行在您的回溯中提到。它是这样说的:

friend = Friend.objects.get(current_user=request.user)

经理的get method旨在精确检索一个对象:

If you know there is only one object that matches your query, you can use the get() method on a Manager which returns the object directly

如果您的查询检索到任何其他数量的对象，则会引发异常(DoesNotExist 的特定于模型的子类 - Friend.DoesNotExist 此处 - 如果返回零个对象如果返回多个对象，则为 MultipleObjectsReturned 的子类)。

我怀疑您希望用户能够拥有零个 friend ，还是多个 friend ？使用 filter() method 而不是 get() :

friends = Friend.objects.filter(current_user=request.user)

无论current_user有多少 friend ，这都会起作用。