Django dropdown form submission invalid - django

Question

Hey i am trying to use modelchoicefield to get a dropdown list in html. But the submission of form yields a invalid form. My code is given below.
views.py
class SubjectSelectFormView(View):
form_class = SubjectSelectForm
template_name = 'study/select_subject.html'
def get(self, request):
form = self.form_class(user=request.user)
return render(request, self.template_name, {'form':form})
def post(self, request):
form = self.form_class(request.POST)
if form.is_valid():
subject = models.Subject.objects.get(name=form['name'])
return HttpResponseRedirect('study:quiz', subject.subject_id)
else:
return HttpResponse('<h1>Failed</h1>')
forms.py
class SubjectSelectForm(forms.Form):
name = forms.ModelChoiceField(queryset=Subject.objects.all().order_by('name'), widget=forms.Select())
def __init__(self, *args, **kwargs):
user = kwargs.pop('user', None)
super(SubjectSelectForm,self).__init__(*args, **kwargs)
self.fields['name'].queryset = Subject.objects.filter(user_id=user)
html
{% extends 'basic_home_app/base.html' %}
{% block content %}
<br>
<form class="form-horizontal" action="" method="post" enctype="multipart/form-data">
{% csrf_token %}
{{ form.as_p }}
<input type="submit" value="Start">
</form>
{% endblock %}

Answer 1

First you should always render the same template with the bound form when a posted form is found to not be valid, this way you can display errors to the user:
def post(self, request):
form = ...
if form.is_valid():
...
else:
return render(request, self.template_name, {'form':form})
Inside your template, you can display errors using either:
{{ form.errors }} # all form errors
{{ form.non_field_errors }} # form errors that aren't for one specific field, use this if you're displaying the field errors separately
or
{{ form.name.errors }} # just the errors for one specific field
Second, I assume you want to initialise your form the same way when it's posted as when it's first displayed (empty) to the user via the get() request:
def post(self, request):
form = self.form_class(request.POST, user=request.user) # note the user
Otherwise your form.__init__() method will set as queryset only Subject objects where user_id is None.