Direct assignment to the forward side of a many-to-many set is prohibited. Use emails_for_help.set() instead

问题

I am new to Django and didn't find any reference regarding this issue. I am getting this error when i use many to many field in django model(models.py). i guess the issue is assining m2m filed in view(views.py) from form(forms.py). How to assign m2m field in view.
Django version 2.O python 3.5

models.py

class User(AbstractUser):
 username=models.CharField(max_length=20)
 email = models.EmailField(_('email address'), unique=True)


class Setupuser(models.Model):
 organization=models.CharField(max_length=200,blank=False,null=True)
 emails_for_help = models.ManyToManyField(User)

views.py

class Set_user(FormView):
 template_name="pkm_templates/set_up_user.html"
 form_class = Set_User_Form
 success_url = '/thanks/'
 def form_valid(self, form):
    org = form.cleaned_data.get('organization')
    emails = form.cleaned_data.get("emails_for_help")
    instance = Setupuser(organization=org,emails_for_help=emails)
    instance.save()
    return redirect("/")

forms.py

class Set_User_Form(ModelForm):
  emails_for_help = 
 forms.ModelMultipleChoiceField(queryset=User.objects.all(),
 widget=forms.CheckboxSelectMultiple)
 class Meta:
    model=Setupuser
    fields=["organization","emails_for_help"]

回答1:

You need to get the User object and then add it to emails_for_help field. You can't add an object to ManyToManyField when creating an instance. Have a look at the doc.

class Set_user(FormView):
    template_name="pkm_templates/set_up_user.html"
    form_class = Set_User_Form
    success_url = '/thanks/'

    def form_valid(self, form):
        org = form.cleaned_data.get('organization')
        emails = form.cleaned_data.get("share_email_with")

        users = User.objects.filter(email__in=emails)
        instance = Setupuser.objects.create(organization=org)

        for user in users:
            instance.emails_for_help.add(user)

        return redirect("/")

EDIT

Another way of doing this is to use .set().

class Set_user(FormView):
    template_name="pkm_templates/set_up_user.html"
    form_class = Set_User_Form
    success_url = '/thanks/'

    def form_valid(self, form):
        org = form.cleaned_data.get('organization')
        emails = form.cleaned_data.get("share_email_with")

        users = User.objects.filter(email__in=emails)
        instance = Setupuser.objects.create(organization=org)

        instance.emails_for_help.set(users)

        return redirect("/")

Or you can simply use .add() to add arbitrary number of objects.

class Set_user(FormView):
    template_name="pkm_templates/set_up_user.html"
    form_class = Set_User_Form
    success_url = '/thanks/'

    def form_valid(self, form):
        org = form.cleaned_data.get('organization')
        emails = form.cleaned_data.get("share_email_with")

        users = User.objects.filter(email__in=emails)
        instance = Setupuser.objects.create(organization=org)

        instance.emails_for_help.add(*users)

        return redirect("/")

来源：https://stackoverflow.com/questions/50015204/direct-assignment-to-the-forward-side-of-a-many-to-many-set-is-prohibited-use-e

标签

python

django

django-orm

m2m