Django ModelForm ManyToManyField initial value

Question

I'm using Django 1.11.2 to develop a website. I use ModelForms to edit my model instances on my website. Every field of the form gets the fitting value of the instance I want to edit via 'initial' in my view. It works fine for all fields except ManyToManyFields.

The relevant code looks like this:

models.py:

class model1(models.Model):
    name = models.CharField(max_length=45, blank=False, null=False)

class model2(models.Model):
    name = models.CharField(max_length=45, blank=False, null=False)
    relation = models.ManyToManyField(model1)

the ModelForm in forms.py:

class model2_form(forms.ModelForm):
    class Meta:
        model = model2
        fields = '__all__'

and the view I use to edit model2 intances:

def model2_edit(request, objectid):
    link = 'Model2'
    model2_inst = model2.objects.get(id=objectid)
    form = model2_form(initial={'name': model2_inst.name,
                                'relation': ???})
    if request.method == 'POST':
        f = model2_form(request.POST, instance=model2_inst)
        if f.is_valid():
            f.save()
            return HttpResponseRedirect('/model2')
    return render(request, "edit_db.html",
                  {"form": form, "link":link})

Everytime I edit an instance of model2 via the ModelForm, the 'relations' of the instance that already exist aren't preselected ('initial' isn't working). If I save the form like this without selecting the relations again, they get deleted and that instance of model2 has no relations anymore. At the place of the '???' in my code I tried many ways to get those relations already selected in the form, but I couldn't find a working way.

I hope I managed to describe my problem, thanks in advance for any help or ideas.

score 4 · Accepted Answer · answered Aug 03 '17 at 12:50

4

form = model2_form(initial={'name': model2_inst.name,
                            'relation': [i.id for i in model2_inst.relation.all()]})

answered Aug 03 '17 at 12:50

Anton Shurashov

1,820
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Thank you very much, I thought I tried this, I must've made a mistake. Now it works fine. – Nkls155 Aug 03 '17 at 12:56

score 3 · Answer 2 · answered Aug 03 '17 at 13:04

3

You should provide the instance for GET and POST requests. This way, you do not need to provide initial data - Django will get the values from the instance automatically.

model2_inst = model2.objects.get(id=objectid)
form = model2_form(instance=model2_inst)

answered Aug 03 '17 at 13:04

Alasdair

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Thanks, that makes it even more simple. – Nkls155 Aug 03 '17 at 13:21

Django ModelForm ManyToManyField initial value

2 Answers2