Django：ValueError：在尝试创建干净失败时，无法在ForeignField上分配任何内容

1 回答

• 1

  基于karthikr在评论中的讨论，我找到了一个我认为可以接受的解决方案 . 我当然仍然愿意接受替代方案 .

  我们的想法是在视图中使用逻辑来选择两种形式进行验证：一种形式是标准模型形式，一种是没有ForeignKey字段的模型形式 .

  所以，我的models.py是完全相同的 .

  我的forms.py有两个Model2表单......一个非常简单，一个没有ForeignKey字段，还有一个新的逻辑，可以为ForeignKey动态生成Model1的新实例 . 新表单的清理逻辑只是我以前在Model2Form中放入的干净逻辑：

  #forms.py
  from django import forms
  from django.forms.models import model_to_dict
  
  from .models import Model1, Model2
  
  
  # A ModelForm used for validation purposes only.
  class Model1Form(forms.ModelForm):
      class Meta:
          model = Model1
  
  
  class Model2Form(forms.ModelForm):
      class Meta:
          model = Model2
  
  # This inherits from Model2Form so that any additional logic that I put in Model2Form
  # will apply to it.
  class Model2FormPrime(Model2Form):
      class Meta:
          model = Model2
          exclude = ('related_model1',)
  
      def clean(self):
          cleaned_data = super(Model2Form, self).clean()
  
          if cleaned_data.get('related_model1', None):
              raise Exception('Huh? This should not happen...')
  
          # Don't instantiate field2 if it doesn't exist.
          val = cleaned_data.get('my_field2', None)
          if not val:
              raise forms.ValidationError("My field must exist")
  
          # Generate a new instance of Model1 based on Model2's data
          new_model1 = Model1(my_field1=val)
  
          # validate the Model1 instance with a form form
          validation_form_data = model_to_dict(new_model1)
          validation_form = Model1Form(validation_form_data)
  
          if not validation_form.is_valid():
              raise forms.ValidationError("Could not create a proper instance of Model1.")
  
          # set the Model1 instance to the related model and save it to the database.
          cleaned_data['related_model1'] = new_model1
  
          return cleaned_data
  
      def save(self, commit=True):
          # Best to wait til save is called to save the instance of Model1
          # so that instances aren't created when the Model2Form is invalid
          self.cleaned_data['related_model1'].save()
  
          # Need to handle saving this way because otherwise related_model1 is excluded
          # from the save due to Meta.excludes
          instance = super(Model2FormPrime, self).save(False)
          instance.related_model1 = self.cleaned_data['related_model1']
          instance.save()
  
          return instance
  

  然后我的视图逻辑使用两种形式之一来验证，具体取决于发布数据 . 如果它使用Model2FormPrime并且验证失败，它会将数据和错误移动到常规Model2Form以向用户显示：

  # Create your views here.
  from django.views.generic.edit import CreateView
  from django.http import HttpResponseRedirect
  
  from .forms import Model2Form, Model2FormPrime
  
  
  class Model2CreateView(CreateView):
      form_class = Model2Form
      template_name = 'form_template.html'
      success_url = '/add/'
  
      def post(self, request, *args, **kwargs):
          if request.POST.get('related_model', None):
              # Complete data can just be sent to the standard CreateView form
              return super(Model2CreateView, self).post(request, *args, **kwargs)
          else:
              # super does this, and I won't be calling super.
              self.object = None
  
              # use Model2FormPrime to validate the post data without the related model.
              validation_form = Model2FormPrime(request.POST)
              if validation_form.is_valid():
                  return self.form_valid(validation_form)
              else:
                  # Create a normal instance of Model2Form to be displayed to the user
                  # Insantiate it with post data and validation_form's errors
                  form = Model2Form(request.POST)
                  form._errors = validation_form._errors
                  return self.form_invalid(form)
  

  这个解决方案有效，而且非常灵活 . 我可以为我的模型和基础Model2Form添加逻辑，而不必担心破坏它或违反DRY .

  但是，它有点难看，因为它要求我使用两种形式来完成一项工作，在表单之间传递错误 . 所以，如果有人可以提出任何建议，我肯定会接受替代解决方案 .

  回复于 2024-04-16T12:48:50+08:00