fix(generic): use dal widget only for models with autocomplete endpoint

The generic form overrides the default select widgets with autocomplete
widgets provided by the django autocomplete light app. This can only
work for contenttypes that provide an autocomplete endpoint. We can only
be sure of that for models that inherit from the GenericModel, so we
skip the override for all the others.

Closes: #764

apis_core/generic/forms/__init__.py

@@ -5,6 +5,7 @@
 from crispy_forms.layout import Submit
 from dal import autocomplete
 from apis_core.generic.forms.fields import ModelImportChoiceField
+from apis_core.generic.abc import GenericModel
 
 
 class GenericImportForm(forms.Form):
@@ -85,8 +86,9 @@ def __init__(self, *args, **kwargs):
                 ct = ContentType.objects.get_for_model(
                     self.fields[field]._queryset.model
                 )
-                url = reverse("apis_core:generic:autocomplete", args=[ct])
-                self.fields[field].widget = override_fieldtypes[clsname](
-                    url, attrs={"data-html": True}
-                )
-                self.fields[field].widget.choices = self.fields[field].choices
+                if issubclass(ct.model_class(), GenericModel):
+                    url = reverse("apis_core:generic:autocomplete", args=[ct])
+                    self.fields[field].widget = override_fieldtypes[clsname](
+                        url, attrs={"data-html": True}
+                    )
+                    self.fields[field].widget.choices = self.fields[field].choices