Question

I’m having a strange riddle to solve:

I extended my django-1.4 user-objects with a UserProfile, as described at https://docs.djangoproject.com/en/dev/topics/auth/ and wanted to implement project-specific roles. So my models look like the following:

class UserProfile(models.Model):
   user = models.ForeignKey(User, unique=True)
   projects = models.ManyToManyField(Project, through='UserProjectRole')
   [...]

class UserProjectRole(models.Model):
   userProfile = models.ForeignKey(UserProfile)
   project = models.ForeignKey(Project)
   group = models.ForeignKey(Group)
   [...]

I needed to pass a css-class, so I created a model-form for UserProjectRole and implemented the userProfile-Field with a widget:

class ProjectRoleForm(forms.ModelForm):
   userProfile = forms.ModelMultipleChoiceField(label='Users',
      queryset=UserProfile.objects.all(),
      widget=forms.SelectMultiple(attrs={'class': 'select-multiple'}))

   class Meta:
       model = UserProjectRole

The form is presented correctly, however, it’s crashing during save-process with the following error

Cannot assign "[<UserProfile: MyUser>]": "UserProjectRole.userProfile" must be a "UserProfile" instance.

Does anyone have an idea?

Answer 1

My guess is it’s because you are using a forms.SelectMultiple widget. Which gives you a list of UserProfile instances ( [<UserProfile: MyUser>] ) and not a single UserProfile instance which is of course required to set on a ForeignKey field (UserProjectRole.userProfile). Thus I suggest to try using a forms.Select widget instead.