Django - Trying to pass an instance of a model field to a form field

Question

I'm going to do my best not to sound like a real dummy, but no promises. I am a paramedic and I'm trying to make an app to document unit checks electronically.I have a model field that is foreign keyed to a few other models in my project. This field designates the unit the user is staffing for that day. I want the user to choose the unit he/she is staffing that day and have that information auto-fill any forms filled out for that session. I've tried storing the object using sessions and I get this "Object of type 'MedicUnit' is not JSON serializable". I've used the model_to_dict method and tried to pass the string of the unit name through the form_valid method but I get this "Cannot assign "'Medic 2'": "DailyCheck.medic_unit_number" must be a "MedicUnit" instance." I'm relatively new to programming and Django and this seems like a very easy problem to fix, but my google searching skills are not getting me anywhere. Here is my code:

Model.py for the origin of the unit_name model field

class MedicUnit(models.Model):
    unit_name = models.CharField(max_length=50, default='')
    is_active = models.BooleanField(default=True)

    def __str__(self):
        return self.unit_name

Model.py for one of the foreign key references to the unit_name

class DailyCheck(models.Model):
    daily_user = models.ForeignKey(User, on_delete=models.PROTECT)
    record_date = models.DateTimeField(auto_now=True)
    medic_unit_number = models.ForeignKey('components.MedicUnit', related_name='medic_unit_number', on_delete=models.PROTECT, default='')
    unit_property_number = models.ForeignKey('components.Vehicle', related_name='unit_property_number', on_delete=models.PROTECT, default='')
    mileage = models.IntegerField(default=0)
    narc_seal_number = models.IntegerField(default=0)
    emergency_lights = models.BooleanField()
    driving_lights = models.BooleanField()
    red_bag = models.BooleanField()
    LP_15 = models.BooleanField()
    BLS_bag = models.BooleanField()
    RTF_bag = models.BooleanField()
    suction = models.BooleanField()
    oxygen = models.BooleanField()
    free_text = models.TextField(default='')

views.py for the directly above model

def check_home_view(request):
    if request.method == 'POST':
        form = ChooseMedicUnit(request.POST or None)
        if form.is_valid():
            unit_name = form.cleaned_data.get('medic_unit_number')
            request.session['unit_name'] = model_to_dict(unit_name)
            print(request.session['unit_name'])
            return redirect('daily')
    else:
        form = ChooseMedicUnit()
    return render(request, 'checks/checks_home.html', {'form':form})

class checkAdd(CreateView):
    model = DailyCheck
    fields = ['unit_property_number', 'mileage', 'narc_seal_number', 'emergency_lights', 'driving_lights', 'red_bag', 'LP_15', 'BLS_bag', 'RTF_bag', 'suction', 'oxygen', 'free_text']
    success_url = '/checks'

    def form_valid(self, form):
        form.instance.daily_user = self.request.user
        form.instance.medic_unit_number = self.request.session['unit_name']['unit_name']
        return super().form_valid(form)

forms.py

class ChooseMedicUnit(forms.ModelForm):
    class Meta:
        model = DailyCheck
        fields = ['medic_unit_number']

Answer 1

I think you can use MedicUnit.id. This should be sufficient to resolve the issue of initializing the field from the session in other forms:

def check_home_view(request):
    if request.method == 'POST':
        form = ChooseMedicUnit(request.POST or None)
        if form.is_valid():
            request.session['unit_name'] = form.cleaned_data.get('medic_unit_number').id  # see here
            print(request.session['unit_name'])
            return redirect('daily')
    else:
        form = ChooseMedicUnit()
    return render(request, 'checks/checks_home.html', {'form':form})

Answer 2

Thank you so much for the answer Andrey. I will try that too. I found that all I had to do was import the MedicUnit model to my view and change my form_valid method to the following:

def form_valid(self, form):
        form.instance.daily_user = self.request.user
        form.instance.medic_unit_number = MedicUnit.ojbects.get(pk=self.request.session['unit_name']['id'])
        return super().form_valid(form)

Apparently sessions cannot store objects since after Django 1.5 I think. Someone may have to fact check me on that. So I referenced an instance of the object with a dictionary value from the model_to_dict data stored in the session with the MedicUnit.object.get call.

If you are having the same problem, you can print the session info to the terminal with a print statement just like in my check_home_view function view. I used that info to see what key was necessary to call primary key number.

I will check Andrey's solution later today and see how well that works. It seems a bit cleaner than my solution.