如何获取模型表单的实例并将其分配给视图中的键？

Question

在表单处理期间，当用户从下拉列表中选择一个值时，我希望能够在其基础模型的模型对象上设置外键字段。

models.py

class Question(models.Model):
    question = models.CharField(max_length=200)

class Teacher(models.Model):
        name = models.CharField(max_length=200)
        l_name = models.CharField(max_length=200)
    
class Student_Answer(models.Model):
    teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE)   
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    answer = models.SmallIntegerField(choices=RATING_CHOICES)

例如，我在模型A中有五个记录，在模型B中有两个记录，并且我有两个模型表单。

forms.py

class AnswerForm(ModelForm):
    class Meta:
        model = Student_Answer
        fields = ('answer',)
        widgets = { 'answer': RadioSelect(choices=RATING_CHOICES),}

class TeacherForm(ModelForm):
    name = ModelChoiceField(queryset=Teacher.objects.all())
    class Meta:
        model = Teacher
        fields = ('name',)

对于问题，我只是直接在视图中分配它们，然后在验证后将实例交给外键。现在，如果我对 Teacher 做同样的事情，我的意思是 teacher = Teacher.objects.get(id=2) 然后 choice.teacher = teacher 它会完美地工作。但这不是我想要的。教师将由用户选择。我正在寻找类似下面视图的方式。

views.py

def index(request):
question1 = Question.objects.get(id=6)
question2 = Question.objects.get(id=7)
if request.method == "POST":
    teacher_form = TeacherForm(request.POST)
    form = AnswerForm(request.POST, prefix='question1')
    form1 = AnswerForm(request.POST, prefix='question2')

    if (form.is_valid):
        choice = form.save(commit=False)
        choice.question = question1
        choice.teacher = teacher_form
        choice.save()

        choice = form1.save(commit=False)
        choice.teacher = teacher_form
        choice.question = question2
        choice.save()

        return HttpResponseRedirect('/submited/')

else:
    teacher_form = TeacherForm()
    form = AnswerForm(prefix='question1')
    form1 = AnswerForm(prefix='question2')

context = {
    'teacher_form': teacher_form,
    'form': form,
    'form1': form1,
    'all_questions': Question.objects.all(),
}
return render(request, 'index.html', context)

上面例子的问题是这个错误：

ValueError: Cannot assign "<TeacherForm bound=True, valid=Unknown, fields=(name)>": "Student_Answer.teacher" must be a "Teacher" instance.

如果我包含实例 choice.teacher = teacher_form.instance 那么就会出现这个错误：

Exception Value:    
save() prohibited to prevent data loss due to unsaved related object 'teacher'.

如果我在验证后将表格保存在第一行，它将为教师创建一条新记录 class。我不想保存新记录，我只想将所选值存储在模板中并将该值存储为 Student_Answer class。有办法解决这个问题吗？

index.html

<form action="{% url 'evaluation:index'%}" method="POST">
  {% csrf_token %}
  {{ teacher_form }}
  {{ all_questions.0 }}
  {{ form }}
  {{ all_questions.1}}
  {{ form1 }}
  
  <input type="submit" value="Vote">
</form>

Answer 1

首先-您的观点存在严重问题。您正在使用多种形式（这并不罕见且很有可能）但您只验证了一个 - 但您必须验证所有这些。有一篇关于这样做的好文章，如果我找到它，我会在更新中 link 它。您的第二个错误正是因为它而出现 - 您试图从未经验证的表单设置实例。

 if all([form.is_valid(), form1.is_valid(), teacher_form.is_valid()]):

其次，是的，您不想 save() 那个教师表格，您甚至不需要它是一个 ModelForm，只需 forms.Form 和 ModelChoiceField 就可以了。您只需要验证它然后访问它的 cleaned_data

# I'm renaming field to 'teacher' since 'name' is poor choice for Teacher object
teacher = teacher_form.cleaned_data['teacher']

最后，对于一些问题形式，您可能需要一个模型形式集 (2-3) 常量形式可能适用于当前方法，但更多或不同数量的问题会让人非常烦恼。

表单集：https://docs.djangoproject.com/en/3.1/topics/forms/modelforms/#model-formsets

如何获取模型表单的实例并将其分配给视图中的键？

how to get instance of a model form and assign it to its key in view?

django

modelform