Django：ValueError：无法创建表单域，因为它的相关模型尚未加载 [英] Django: ValueError: Cannot create form field because its related model has not been loaded yet

问题描述

我正在处理一个Django项目中遇到麻烦。我现在有两个应用程序，这需要很大的重叠。我真的只启动了第二个项目（称为工作流程），我试图为该应用程序制作第一个表单。我的第一个应用程序称为 po 。在工作流程应用程序中，我有一个名为 WorkflowObject 的类，（现在）只有一个属性 - PurchaseOrder 的外键，它在 po / models.py 中定义。我从po.models import PurchaseOrder 导入了的类。

我想要做的是有一个用户创建一个新的 PurchaseOrder 的页面。这工作正常（这与我在 PurchaseOrder 应用程序中使用的形式相同），然后使用该类的实例来创建一个 WorkflowObject 。现在的问题是，我收到错误： ValueError：不能为'购买'创建表单字段，因为它的相关模型PurchaseOrder尚未加载。我真的不知道从哪里开始。它工作正常（允许我创建一个新的 PurchaseOrder 并转发到一个url与其主键在url），直到我添加了应该允许我创建一个新的 WorkflowObject 。我会在这里给出具体的看法：

  from django.http import HttpResponse，HttpResponseRedirect 
 from django.shortcuts import render，get_object_or_404 
从django_tables2导入RequestConfig 
从po.models import PurchaseOrderForm，PurchaseOrder 
 from workflow.models import POObject，WorkflowForm 
 
 
 def new2请求，号码）：
 po = PurcchaseOrder.objects.get（pk = number）
如果request.method =='POST'：
 form = WorkflowForm（request.POST）
如果form.is_valid（）：
 new_flow = form.save（）
 return HttpResponse（'Good'）
 else：
 return render（request，'new-workflow。 html'，{'form'：form，'purchase'：po}）
 else：
 form = WorkflowForm（）
 return render（request，'new-workflow.html'，{ 'form'：form，'purchase'：po}）
  

导致错误（或至少是其中的一行如下所示：

  class WorkflowForm（ModelForm）：
 purchase = forms.ModelChoiceField（queryset = PurchaseOrder .objects.all（））
  

编辑：
我似乎做了一个非常noob错误，并在我的 WorkflowObject 的定义中包含括号，也就是说我已经说过 purchase = models.ForeignKey（'PurchaseOrder'），而不是 purchase = models.ForeignKey（PurchaseOrder）

解决方案

p>首先，你可以尝试减少代码：

  def new2（request，number）： 
 po = PurcchaseOrder.objects.get（pk = number）
 
 form = WorkflowForm（request.POST或None）
如果form.is_valid（）：
 new_flow = form.save（）
 return HttpResponse（'Good'）
 else：
 return render（request，'new-workflow.html'，{'form'：form，'purchase' ：po}）
  

其次，我不明白为什么你在其他情况下写了 forms.ModelChoiceField（...）另一种情况 ModelForm instance forms.ModelForm ？

I'm having some trouble with a Django project I'm working on. I now have two applications, which require a fair bit of overlap. I've really only started the second project (called workflow) and I'm trying to make my first form for that application. My first application is called po. In the workflow application I have a class called WorkflowObject, which (for now) has only a single attribute--a foreign key to a PurchaseOrder, which is defined in po/models.py. I have imported that class with from po.models import PurchaseOrder.

What I'm trying to do is have a page where a user creates a new PurchaseOrder. This works fine (it's the same form that I used in my PurchaseOrder application), and then uses that instance of the class to create a WorkflowObject. The problem now, is that I get the error: ValueError: Cannot create form field for 'purchase' yet, because its related model 'PurchaseOrder' has not been loaded yet. I'm really not sure where to start with this. It was working ok (allowing me to create a new PurchaseOrder and forward to a url with its primary key in the url) until I added the view that should allow me to create a new WorkflowObject. I'll put that specific view here:

from django.http import HttpResponse, HttpResponseRedirect
from django.shortcuts import render, get_object_or_404
from django_tables2 import RequestConfig
from po.models import PurchaseOrderForm, PurchaseOrder
from workflow.models import POObject, WorkflowForm


def new2(request, number):
 po=PurcchaseOrder.objects.get(pk=number)
 if request.method == 'POST':
   form = WorkflowForm(request.POST)
   if form.is_valid():
      new_flow = form.save()
      return HttpResponse('Good')
   else:
      return render(request, 'new-workflow.html', {'form': form, 'purchase': po})
  else:
    form = WorkflowForm()
    return render(request, 'new-workflow.html', {'form': form, 'purchase': po})

The lines of code that seem to be causing the error (or at least, one of the lines that is shown in the traceback) is:

class WorkflowForm(ModelForm):
   purchase = forms.ModelChoiceField(queryset = PurchaseOrder.objects.all())

EDIT: I seem to have made a very noob mistake, and included parentheses in my definition of WorkflowObject, that is, I had said purchase=models.ForeignKey('PurchaseOrder'), instead of purchase=models.ForeignKey(PurchaseOrder)

解决方案

Firstly, you can try reduce code to:

def new2(request, number):
    po=PurcchaseOrder.objects.get(pk=number)

    form = WorkflowForm(request.POST or None)
    if form.is_valid():
        new_flow = form.save()
        return HttpResponse('Good')
    else:
        return render(request, 'new-workflow.html', {'form': form, 'purchase': po})

Secondly, I not understood why you at other case wrote forms.ModelChoiceField(...) and another case ModelForm instance forms.ModelForm ?

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