根据ForeignKey关系过滤Django表单中的ModelChoiceField选项

Question

在我的django项目中，我创建了三个模型类。 “ Subtopic”类与“ Chapter”类具有ForeignKey关系，而“ SAQ”类与“ Chapter”类和“ Subtopic”类具有ForeignKey关系。

#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"]

我试图使用Django ModelForm为“模型SAQ”创建表单，以便对于与特定章节实例相关联的每个“ SAQ表单”，模型“ Subtopic”的选择字段将仅包含该特定章节实例的那些子主题。

#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',
        ]

创建表单的django视图功能如下。

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”形式的选择字段显示所有章节实例的所有子主题。 任何建议都将非常有帮助。

Answer 1

我建议重写表单init并传递Chapter实例，以便您可以过滤子主题queryset。

示例（未经测试，可能包含错字）：

#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，您的视图应将Chapter实例传递给表单：

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