根據ForeignKey關系過濾Django表單中的ModelChoiceField選項

Question

在我的django項目中，我創建了三個模型類。 “ Subtopic”類與“ Chapter”類具有ForeignKey關系，而“ SAQ”類與“ Chapter”類和“ Subtopic”類具有ForeignKey關系。

#models.py

from django.db import models
class Chapter(models.Model):
    chapter_serial = models.IntegerField(null=False, help_text="Chapter No.")
    slug = models.SlugField(unique=True, blank=True)
    chapter_name = models.CharField(max_length=120)

    class Meta:
        ordering = ["chapter_serial"]

    def get_saq_list_url(self):
        return reverse("cms:saq_list", kwargs={"chap_slug":self.slug})

class Subtopic(models.Model):
    subtopic_serial = models.IntegerField(null=False)
    title = models.CharField(max_length=240)
    chapter = models.ForeignKey('Chapter', on_delete=models.CASCADE)

    class Meta:
        ordering = ["subtopic_serial"]

class SAQ(models.Model):
    question_serial = models.IntegerField(null=False)
    question = models.TextField()
    answer = models.TextField()
    chapter = models.ForeignKey('Chapter', on_delete=models.CASCADE)
    subtopic = models.ForeignKey('Subtopic', on_delete=models.CASCADE, null=True, blank=True)

    class Meta:
        ordering = ["question_serial"]

我試圖使用Django ModelForm為“模型SAQ”創建表單，以便對於與特定章節實例相關聯的每個“ SAQ表單”，模型“ Subtopic”的選擇字段將僅包含該特定章節實例的那些子主題。

#forms.py
from django import forms
from .models import SAQ

class SAQForm(forms.ModelForm):

    class Meta:
        model = SAQ
        fields = [
            'question_serial',
            'question',
            'answer',
            'important',
            'remarks',
            'subtopic',
        ]

創建表單的django視圖功能如下。

from django.shortcuts import render, get_object_or_404, redirect
from .models import SAQ, Chapter, Subtopic
from .forms import SAQForm
from django.http import HttpResponseRedirect

def saq_create(request, chap_slug=None):
    chapter_instance = get_object_or_404(Chapter, slug=chap_slug)
    form = SAQForm(request.POST or None)
    if form.is_valid():
        instance = form.save(commit=False)
        instance.chapter = chapter_instance
        instance.save()
        return HttpResponseRedirect(chapter_instance.get_saq_list_url())
    context = {
        "form":form,
        "chapter_instance":chapter_instance,
    }
    return render(request, 'cms/saq_form.html', context)

使用此配置，“ Subtopic”形式的選擇字段顯示所有章節實例的所有子主題。 任何建議都將非常有幫助。

Answer 1

我建議重寫表單init並傳遞Chapter實例，以便您可以過濾子主題queryset。

示例（未經測試，可能包含錯字）：

#forms.py
from django import forms
from .models import SAQ

class SAQForm(forms.ModelForm):

    class Meta:
        model = SAQ
        fields = [
            'question_serial',
            'question',
            'answer',
            'important',
            'remarks',
            'subtopic',
        ]

    def __init__(self, chapter, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['subtopic'].queryset = \
            self.fields['subtopic'].queryset.filter(chapter=chapter)

然后，您的視圖應將Chapter實例傳遞給表單：

chapter_instance = get_object_or_404(Chapter, slug=chap_slug)
form = SAQForm(chapter_instance, request.POST or None)