python - Save Many-To-Many Field Django Forms

Question

I have a Many-To-Many relationship between a Course and Tutor model. I am trying to make it so that when you use a form to create a record for a new Tutor, you can select the courses they can teach. I tried using and modifying the code from this previous question as best I could, but I don't fully understand it so I'm sure I didn't do it right. When the form is submitted, it won't save the link between the Courses and Tutor. What do I need to change about the code to make it save?

models.py

class Tutor(models.Model):
    FirstName = models.CharField(max_length=50)
    LastName = models.CharField(max_length=50)
    Email = models.EmailField(max_length=100)
    PhoneNumber = models.CharField(max_length=10, )
    RequestedHours = models.DecimalField(max_digits=3, decimal_places=1)

class Course(models.Model):
    SubjectID = models.ForeignKey(Subject, related_name='subjectCourse')
    Department = models.CharField(max_length=4)
    Number = models.CharField(max_length=4)
    Name = models.CharField(max_length=200)
    TutorForCourse = models.ManyToManyField(Tutor)

forms.py

class TutorForm(forms.ModelForm):
    class Meta:
        model = Tutor
        fields = ('FirstName', 'LastName', 'Email', 'PhoneNumber', 
           'RequestedHours',)
        labels = {
            'FirstName': 'First Name',
            'LastName': 'Last Name',
            'Email': 'Email',
            'PhoneNumber': 'Phone Number',
            'RequestedHours': 'Requested Hours',
        }

    courses = forms.ModelMultipleChoiceField(queryset=Course.objects.all())

    def __init__(self, *args, **kwargs):
        # Only in case we build the form from an instance
        # (otherwise, 'toppings' list should be empty)
        if kwargs.get('instance'):
            # We get the 'initial' keyword argument or initialize it
            # as a dict if it didn't exist.
            initial = kwargs.setdefault('initial', {})
            # The widget for a ModelMultipleChoiceField expects
            # a list of primary key for the selected data.
            initial['courses'] = [t.pk for t in 
                kwargs['instance'].course_set.all()]

        forms.ModelForm.__init__(self, *args, **kwargs)

    # Overriding save allows us to process the value of 'toppings' field
    def save(self, commit=True):
        # Get the unsaved Pizza instance
        instance = forms.ModelForm.save(self, False)

        # Prepare a 'save_m2m' method for the form,
        old_save_m2m = self.save_m2m

        def save_m2m():
            old_save_m2m()
            # This is where we actually link the pizza with toppings
            instance.course_set.clear()
            for course in self.cleaned_data['courses']:
                instance.course_set.add(course)

        self.save_m2m = save_m2m

        # Do we need to save all changes now?
        if commit:
            instance.save()
            self.save_m2m()

        return instance

views.py

@login_required
def tutor_new(request):
    if request.method == "POST":
        form = TutorForm(request.POST)
        if form.is_valid():
            tutor = form.save(commit=False)
            tutor.save()
            tutors = Tutor.objects.filter()
            return render(request, 'portfolio/tutor_list.html',
                          {'tutors': tutors})
    else:
        form = TutorForm()
        # print("Else")
    return render(request, 'portfolio/tutor_new.html', {'form': form})

Answer 1

Updated answer

The problem is in save method. You save instance with commit=False but your instance saved when if commit: so it's not saving now.

Just commented out if commit: and it will be saved well.

def save(self, commit=True):
    # Get the unsaved Pizza instance
    instance = forms.ModelForm.save(self, False)

    # Prepare a 'save_m2m' method for the form,
    old_save_m2m = self.save_m2m

    def save_m2m():
        old_save_m2m()
        # This is where we actually link the pizza with toppings
        instance.course_set.clear()
        for course in self.cleaned_data['courses']:
            instance.course_set.add(course)

    self.save_m2m = save_m2m

    # Do we need to save all changes now?
    # Just like this
    # if commit:
    instance.save()
    self.save_m2m()

    return instance