Django 错误：需要字段“...”的值才能使用这种多对多关系

Question

保存表单时出现此错误： "" 需要为字段 "surveythread" 设置一个值，然后才能使用这种多对多关系。

模型.py：

class SurveyResult(models.Model):
    stay = models.OneToOneField(Stay, related_name='survey')
    created = models.DateTimeField(default=datetime.now)
    vote = models.BooleanField(default=False)
    vote_service = models.BooleanField(default=False)
    comment = models.TextField(blank=True, null=True)

    def getThreads(self):
        return SurveyThread.objects.filter(parent_survey = self)

    threads = property(getThreads)

    def __unicode__(self):
        return self.vote and 'Good' or 'Bad'

    class Meta:
        get_latest_by = '-created'

class SurveyThread(models.Model):
    survey = models.ManyToManyField(SurveyResult, related_name='parent_survey')
    email = models.EmailField(max_length=200)
    comment = models.TextField(blank=True, null=True)

views.py：

survey_list = SurveyResult.objects.filter(stay__guest__user=request.user) \
                                      .select_related('stay', 'stay__guest')

forms = {}
for survey in survey_list:
  forms[survey] = SurveyThreadForm(data=request.POST or None, survey=survey)

  if forms[survey].is_valid():
    instance = forms[survey].save()
    return redirect('.')

forms.py

class SurveyThreadForm(forms.Form):

    comment = forms.CharField(required=False, widget=forms.Textarea)

    def __init__(self, *args, **kwargs):
        self.survey = kwargs.pop('survey', None)

        if not self.survey:
            raise NotImplementedError("SurveyResult object is required at this moment")

        super(SurveyThreadForm, self).__init__(*args, **kwargs)

        self.fields['comment'].label = "Message to send to guest:"

    def save(self, commit=True):
        s = SurveyThread()
        s.survey = self.survey
        s.email = "test@test.com"
        s.comment = self.cleaned_data['comment']

        if commit:
            s.save()
        return s

错误信息：

ValueError at /
"<SurveyThread: SurveyThread object>" needs to have a value for field "surveythread" before this many-to-many relationship can be used.
Request Method: POST
Request URL:    http://127.0.0.1:8000/
Django Version: 1.5.1
Exception Type: ValueError
Exception Value:    
"<SurveyThread: SurveyThread object>" needs to have a value for field "surveythread" before this many-to-many relationship can be used.
Exception Location: /Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/django/db/models/fields/related.py in __init__, line 586
Python Executable:  /Users/tlovett1/.virtualenvs/guestretain/bin/python
Python Version: 2.7.2
Python Path:    
['/Users/tlovett1/guestretain',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python27.zip',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/plat-darwin',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/plat-mac',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/plat-mac/lib-scriptpackages',
 '/Users/tlovett1/.virtualenvs/guestretain/Extras/lib/python',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/lib-tk',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/lib-old',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/lib-dynload',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages',
 '/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/PIL']
Server time:    Sun, 7 Jul 2013 10:22:55 -0500

追溯：

Traceback Switch to copy-and-paste view

/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/django/core/handlers/base.py in get_response
                        response = callback(request, *callback_args, **callback_kwargs) ...
▶ Local vars
/Users/tlovett1/guestretain/retain/apps/profiles/utils.py in _wrapped_view
                    return view_func(request, *args, **kwargs) ...
▶ Local vars
/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/endless_pagination/decorators.py in decorated
            return view(request, *args, **kwargs) ...
▶ Local vars
/Users/tlovett1/guestretain/retain/apps/dashboard/views.py in dashboard
            instance = forms[survey].save() ...
▶ Local vars
/Users/tlovett1/guestretain/retain/apps/surveys/forms.py in save
        s.survey = self.survey ...
▶ Local vars
/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/django/db/models/fields/related.py in __set__
        manager = self.__get__(instance) ...
▶ Local vars
/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/django/db/models/fields/related.py in __get__
            through=self.field.rel.through, ...
▶ Local vars
/Users/tlovett1/.virtualenvs/guestretain/lib/python2.7/site-packages/django/db/models/fields/related.py in __init__
                                 (instance, source_field_name)) ...
▶ Local vars

我是 Django 和 Python 的新手。如果需要，我可以发布调试跟踪或迁移文件，但我觉得这是一个简单的修复。显然重点是我想为每个调查结果保存多个调查线程。

谢谢！

Answer 1

好的，代码有点乱，我相信你会更好tackling your problem with ModelForms。在我看来问题实际上是行：

s.survey = self.survey

因为s 对象尚未写入数据库，所以访问它的survey ManyToMany 字段可能会产生问题。如果您想将同一组调查从self 复制到s，您应该像这样对它们进行迭代：

如果这产生相同的错误，则尝试先执行s.save()，然后再复制项目：

s.save()
for item in self.survey:
    s.survey.add(item)

您的代码可能仍然是这样的：

def save(self, commit=True):
    s = SurveyThread()
    # these fields aren't problematic
    s.email = "test@test.com"
    s.comment = self.cleaned_data['comment']
    # you can add s.save() here to remove problems associated with object 
    # not yet persisted
    # s.save()
    for item in self.survey:
        s.survey.add(item)
    if commit:
        s.save()
    return s

我可以看到您有一个 if commit: 来持久化该对象，因此请尝试容纳代码以使用它。如果我的答案的第一个版本有效，那么最后你会很好地使用s.save()，如果第二个版本是有效的，那么你将不得不稍微调整代码以坚持commit价值。

希望这会有所帮助！

Answer 2

在forms.py 的这部分代码中，您将SurveyThread 对象上的survey 字段设置为None，但根据您的models.py，它不允许为None：

def save(self, commit=True):
    s = SurveyThread()
    s.survey = None     ### This is the problem
    s.email = "test@test.com"
    s.comment = self.cleaned_data['comment']

    if commit:
        s.save()
    return s

您必须先将survey 设置为SurveyResult 对象，然后才能保存它，或者允许它在模型中为None。

我想你想把它改成：

s.survey = self.survey