Django ModelChoiceField has no plus button

Question

I'm making a Django app with custom users. I've outlined the key components of my problem below, missing code is denoted by '...'. My custom user model has a foreign key relationship as follows:

class MyCustomUser(models.AbstractBaseUser, models.PermissionsMixin)
    ...
    location = models.ForeignKey(Location)

class Location(models.Model)
    name = models.CharField(max_length=50, blank=True, null=True)

I've written a custom user form that includes this field as follows:

class MyCustomUserCreationForm(models.ModelForm)
    ...
    location = forms.ModelChoiceField(Location.objects.all())

This all appears to be working correctly, however, there is no plus button to the right of the select field for location. I want to be able to add a location when I create a user, in the same way that you can add polls when creating choices in the Django tutorial. According to this question, I might not see the green plus if I don't have permission to change the model, but I am logged in as a superuser with all permissions. Any idea what I'm doing wrong?

Answer 1

You need to set a RelatedFieldWidgetWrapper wrapper in your model form:

The RelatedFieldWidgetWrapper (found in django.contrib.admin.widgets) is used in the Admin pages to include the capability on a Foreign Key control to add a new related record. (In English: puts the little green plus sign to the right of the control.)

class MyCustomUserCreationForm(models.ModelForm)
    ...
    location = forms.ModelChoiceField(queryset=Location.objects.all())

    def __init__(self, *args, **kwargs):
        super(MyCustomUserCreationForm, self).__init__(*args, **kwargs)
        rel = ManyToOneRel(self.instance.location.model, 'id') 
        self.fields['location'].widget = RelatedFieldWidgetWrapper(self.fields['location'].widget, rel, self.admin_site)

I could make a mistake in the example code, so see these posts and examples:

• RelatedFieldWidgetWrapper
• More RelatedFieldWidgetWrapper – My Very Own Popup
• Django admin - How can I add the green plus sign for Many-to-many Field in custom admin form
• How can I manually use RelatedFieldWidgetWrapper around a custom widget?
• Django: override RelatedFieldWidgetWrapper

Answer 2

I have created method based on the answers above:

def add_related_field_wrapper(form, col_name):
    rel_model = form.Meta.model
    rel = rel_model._meta.get_field(col_name).rel
    form.fields[col_name].widget = 
    RelatedFieldWidgetWrapper(form.fields[col_name].widget, rel, 
    admin.site, can_add_related=True, can_change_related=True)

And then calling this method from my form:

class FeatureForm(forms.ModelForm):
    offer = forms.ModelChoiceField(queryset=Offer.objects.all(), required=False)
    package = forms.ModelChoiceField(queryset=Package.objects.all(), required=False)
    def __init__(self, *args, **kwargs):
        super(FeatureForm, self).__init__(*args, **kwargs)
        add_related_field_wrapper(self, 'offer')
        add_related_field_wrapper(self, 'package')

That works fine on Django 1.8.2.