如何链接在表单中选择的 Django 外键与内联表单？

Question

Introduction

Hello. I am a self-taught novice python/Django coder working on my family business truck maintenance Django app, I have some of the basics of Django and python3 down. but other basics escape me as everything I am learning has been done for practicality sake and not built from the foundations of these languages.

I have the following types of models:

• Truck - a single truck
• Service - a single instance of a repair/maintenance service for a single truck
• Photo - a single picture from the photologue app
• PhotoExtended - an add-on model one-to-one with Photo where it can be linked to a truck and/or a service. A photo will ALWAYS be associated with a truck, but may or may not be associated with a service.

relevant models.py:

class PhotoExtended(models.Model):

    # Link back to Photologue's Photo model.
    photo = models.OneToOneField(Photo, related_name='extended', on_delete=models.RESTRICT)
    truck = models.ForeignKey('Truck', on_delete=models.CASCADE, 
                        default = DEFAULT_TRUCK_ID, help_text="Truck in the picture.")
    service = models.ForeignKey('Service', on_delete=models.PROTECT,
                        null=True, blank=True, help_text="Service being performed or finished in the picture.")
    receipt = models.BooleanField(help_text="Is the picture for a receipt?", null=True, default=False)
    
    # Boilerplate code to make a prettier display in the admin interface.
    class Meta:
        verbose_name = u'Associated photo'
        verbose_name_plural = u'Associated photos'

    def __str__(self):
        return self.photo.title

The problem at hand

In the admin form set up, I have a nice service form with an inline PhotoExtended form; however, I have not figured out how to update the PhotoExtended truck foreign key with the value selected in the form. A lot of the answers I found date back to earlier versions of Django, so updating them to the current specifications hasn't worked for me.

shortened admin.py:

from django.contrib import admin
from django.utils.translation import ugettext_lazy
from django.urls import reverse
from photologue.admin import PhotoAdmin as PhotoAdminDefault, PhotoAdminForm
from photologue.models import Photo
from .models import Truck, Service, PhotoExtended

class PhotoExtendedInline(admin.StackedInline):
    model = PhotoExtended
    max_num=4
    extra=0
    can_delete = True
class PhotoAdmin(PhotoAdminDefault):
    inlines = [PhotoExtendedInline, ]
    view_on_site=False

class ServiceAdmin(admin.ModelAdmin):
...
    inlines = [
        PhotoExtendedInline,
    ]
    date_hierarchy = 'service_date'
...

In short, I need a way to access the information that was entered in the parent form and use it to prepopulate the Truck foreign key in the inline form. The Service foreign key gets linked automatically, but not the one for the Truck.

I would be grateful for any and all help with my question. Thank you!

Answer 1

I figured it out. Kind of. It only works for already saved forms.

First, I had to add add a class to the ServiceAdmin form:

    def get_form(self, request, obj=None, **kwargs):
        request._service_obj = obj
        return super(ServiceAdmin, self).get_form(request, obj, **kwargs)

Then, for the Inline form, I had to add a foreignkey form method:

    def formfield_for_foreignkey(self, db_field, request=None, **kwargs):
        formfield = super(PhotoExtendedInline_Service, self).formfield_for_foreignkey(db_field, request, **kwargs)
        if db_field.name == 'truck':
            if request._service_obj is not None:
                formfield.queryset = formfield.queryset.filter(service__exact = request._service_obj)
            else:
                formfield.queryset = formfield.queryset.none()
        return formfield

I hope this helps out future coders!