Django保存具有唯一约束的表单

Question

I have a simple Profile model linked to Djang user model that keep alias.

Alias has a unique constraint in the model.

To update the alias, I created a model form, but can't figure out how to exclude the unique constraint when the user just push the submit button with no change to the alias. The form raise an error because of unique constraint.

Here's the model and form definition with part of the view that handle the form:

models.py

class Profile(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE
    )

    alias = models.CharField(
        "Alias",
        max_length=50,
        unique=True,
        null=True
    )

forms.py

class ProfileForm(ModelForm):
    class Meta:
        model = Profile
        fields = ['alias', ]

And the views.py

def membership(request):
    if request.method != 'POST':
        profile = Profile.objects.get(user=request.user)
        form = ProfileForm(initial={'alias': profile.alias, 'user': request.user})
    elif request.POST.get('profile_update', None) == 'profile_update':
        form = ProfileForm(request.POST)
        if form.is_valid():
            form.save()

Answer 1

You need to pass the instance to the form. I've also switched out the alias key in the GET path's form with the instance usage.

def membership(request):
    profile = Profile.objects.get(user=request.user)
    if request.method != 'POST':
        form = ProfileForm(instance=profile, initial={'user': request.user})
    elif request.POST.get('profile_update', None) == 'profile_update':
        form = ProfileForm(request.POST, instance=profile)
        if form.is_valid():
            form.save()