CODEWITHSUNDEEP
pythondjangodjango-modelsdjango-forms
Saša Kalaba
Saša Kalaba

Reputation: 4421

How to change data in Django ModelForm?

models.py

class Playlist(models.Model):
    name = models.CharField(max_length=50)
    num_of_songs = models.IntegerField(max_length=15)
    duration = models.IntegerField()
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    songs = models.ManyToManyField("Song", blank=True)

forms.py

class PlaylistEditForm(forms.ModelForm):
    class Meta:
        model = Playlist
        fields = ['name', 'songs']

I calculate duration and num_of_songs based on the songs I get from the form. But I do that calculation from a view.

views.py

playlist = Playlist.objects.get(id=playlist_id)

if request.method == 'POST':
    form = PlaylistEditForm(request.POST, instance=playlist)
    if form.is_valid():
        form.save()
        playlist.duration = playlist.songs.aggregate(Sum('duration'))['duration__sum'] or 0
        playlist.num_of_songs = playlist.songs.count()
        playlist.save()

I want to calculate duration and num_of_songs inside a form.

Upvotes: 0

Views: 2295

Answers (2)

biodiv
biodiv

Reputation: 627

Is there any reason not to do it in the models save() method? If you have it in the forms save() method, the duration and num_of_songs in the database will not get updated if you save the model instance other than from the modelform.

class Playlist(models.Model):
    name = models.CharField(max_length=50)
    num_of_songs = models.IntegerField(max_length=15)
    duration = models.IntegerField()
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, blank=True)
    songs = models.ManyToManyField("Song", blank=True)

    def save(self, *args, **kwargs):
        if self.pk:
            self.duration = self.songs.aggregate(Sum('duration'))['duration__sum'] or 0
            self.num_of_songs = self.songs.count()
        return super(Playlist, self).save(*args, **kwargs)

You view would be:

if request.method == 'POST':
    form = PlaylistEditForm(request.POST, instance=playlist)
    if form.is_valid():
        playlist = form.save()

Upvotes: 0

Pynchia
Pynchia

Reputation: 11596

you can move the calculation to the form overriding the form's save method

def save(self, commit=True):
    instance = super(PlaylistEditForm, self).save(commit=False)
    instance.duration = instance.songs.aggregate(Sum('duration'))['duration__sum'] or 0
    instance.num_of_songs = instance.songs.count()
    if commit:
        instance.save()
    return instance

and your view becomes

playlist = Playlist.objects.get(id=playlist_id)

if request.method == 'POST':
    form = PlaylistEditForm(request.POST, instance=playlist)
    if form.is_valid():
        form.save()

Please refer to Django's official docs for further info.

Upvotes: 2

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