Django 返回多个对象

Question

所以我在下面有我的代码，每当我在管理中运行它并尝试查看该对象时 returns 和错误：

异常类型：MultipleObjectsReturned 异常值：
get() 返回了多个 c2 -- 它返回了 2!

如何解决此错误？

models.py:

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


class c1(models.Model):
    name = models.CharField(max_length=30, default="Other")

    def __str__(self):
        return self.name

class c2(models.Model):
    c1 = models.ForeignKey(c1, on_delete=models.CASCADE)
    name = models.CharField(max_length=30, default="Other")

    def __str__(self):
        return self.name

class c3(models.Model):
    c2 = models.ForeignKey(c2, on_delete=models.CASCADE)
    name = models.CharField(max_length=30, default="Other")

    def __str__(self):
        return self.name

class Task_manager(models.Manager):
    def create_Task(self, title):
        Task1 = self.create(title=title)
        return Task1

class Task(models.Model):
    STATUS = (
       ('ONGOING', 'ONGOING'),
       ('COMPLETED','COMPLETED'),

   )

    search=models.CharField(max_length=300, choices=search_title, default="OTHER")
    c1=models.ForeignKey(c1, on_delete=models.SET_NULL, null=True)
    c2=models.ForeignKey(c2, on_delete=models.SET_NULL, null=True)
    c3=models.ForeignKey(c3, on_delete=models.SET_NULL, null=True)
    title=models.CharField(max_length=30,default="Other")
    created=models.DateTimeField(default=timezone.now())
    objects=Task_manager()
    class Meta:
        ordering = [ '-created']
    def __str__(self):
        return self.title

这是我在 admin.py 中的 ModelAmdin class admin.py 片段：

class TaskAdmin(admin.ModelAdmin):
    film_status.allow_tags = True'''
    form=TaskForm
    list_filter=('c1')
    readonly_fields = ['score','score_fixed','deadline_fixed','created']
    def change_view(self,request,object_id,extra_content=None):
         return super(TaskAdmin,self).change_view(request,object_id)
admin.site.register(Task,TaskAdmin)
admin.site.register(c1)
admin.site.register(c2)
admin.site.register(c3)

您还可以查看 TaskForm class。 forms.py:

class TaskForm(forms.ModelForm):

    class Meta:
        model=Task
        fields='__all__'
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['c1'].queryset = c1.objects.all()
        self.fields['c2'].queryset = c2.objects.get()
        self.fields['c3'].queryset = c3.objects.none()

这是代码的完整错误：

Traceback (most recent call last):
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\contrib\admin\options.py", line 607, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\views\decorators\cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\contrib\admin\sites.py", line 231, in inner
    return view(request, *args, **kwargs)
  File "C:\My_Django_stuff\tada\todo\tasks\admin.py", line 64, in change_view
    return super(TaskAdmin,self).change_view(request,object_id)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\contrib\admin\options.py", line 1641, in change_view
    return self.changeform_view(request, object_id, form_url, extra_context)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\utils\decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\utils\decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\contrib\admin\options.py", line 1522, in changeform_view
    return self._changeform_view(request, object_id, form_url, extra_context)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\contrib\admin\options.py", line 1582, in _changeform_view
    form = ModelForm(instance=obj)
  File "C:\My_Django_stuff\tada\todo\tasks\forms.py", line 14, in __init__
    self.fields['c2'].queryset = c2.objects.get()
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\db\models\manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\sarda\anaconda3\envs\myDjangoEnv\lib\site-packages\django\db\models\query.py", line 419, in get
    raise self.model.MultipleObjectsReturned(

Exception Type: MultipleObjectsReturned at /admin/tasks/task/9/change/
Exception Value: get() returned more than one c2 -- it returned 2!

Answer 1

如果查询集不完全包含一个对象，

QuerySet.get() 将引发异常。 Either an DoesNotExist or an MultipleObjectsReturned。这是设计使然。

您可以通过调用另一个 QuerySet 方法（例如，.first() 来获取第一个对象）使用 try, except 来处理此问题。

Django 返回多个对象

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