Django Modelform doesn't accept selection on POST

Question

The dropdown list appears correctly in the html, However I am unable to figure out why I run into the same error time after time when I try to submit / .

"Select a valid choice. That choice is not one of the available choices."

the problem context

I have two models defined in Django. One CourseModel database to hold all the offered courses and one registration database to link a course to a user.

models.py

from django.db import models
# Create your models here.

class CourseModel(models.Model):
    course = models.CharField(max_length=100)
    date = models.DateField(max_length=100)
    time = models.TimeField()
    location = models.CharField(max_length=100)
    datetime = models.DateTimeField()

class RegistrationModel(models.Model):
    name = models.CharField(max_length=100)
    adress = models.CharField(max_length=100)
    city = models.CharField(max_length=100)
    email = models.EmailField(max_length=100)
    course = models.ForeignKey('self', on_delete=models.CASCADE)

    def __str__(self):
        return self.name

I use modelForm to create a registration form, where the user can subscribe for a course from a dropdown list.

forms.py

from django.forms import ModelForm, RegexField
from home.models import RegistrationModel, CourseModel
from django import forms
import datetime


class RegistrationForm(ModelForm):

    def __init__(self, *args, **kwargs):
        super(RegistrationForm, self).__init__(*args, **kwargs)
        self.fields['course'].queryset = CourseModel.objects.exclude(date__lt=datetime.datetime.today()).values_list('datetime', flat=True)
        self.fields['course'].empty_label = None


    class Meta:
        model = RegistrationModel
        fields = '__all__'

views.py

from django.shortcuts import render, redirect
from home.forms import RegistrationForm
from .models import CourseModel
import datetime

def home(request):
    return render(request, 'home/home.html')


def registration(request):
    if request.method == 'POST':
        form = RegistrationForm(request.POST)
        crs = request.POST.get('course')
        print(crs)
        if form.is_valid():
            cleanform = form.save(commit=False)
            cleanform.course = crs
            cleanform.save()
            return redirect('home')
    else:
        form = RegistrationForm()
    return render(request, 'home/registration.html', {'form': form})

djvg · Answer 1 · 2018-09-12T06:07:05.340

In the RegistrationForm's __init__() method, your self.fields['course'].queryset = ...values_list('datetime', flat=True) returns datetime instances. See values_list() docs.

I believe this may cause the issue. I guess the queryset should return CourseModel instances, based on the Django docs:

ForeignKey is represented by django.forms.ModelChoiceField, which is a ChoiceField whose choices are a model QuerySet.

Also, your RegistrationModel.course field has a foreign key to 'self' instead of the CourseModel. Not sure if that is what you want.

Other examples of setting the field queryset can be found here.

Django Modelform doesn't accept selection on POST

1 Answers1