Allow use of can_delete flag directly in inline definition

The previous README had instructions about preventing the deletion of
inlined models by overriding the `has_delete_permission` method on a
custom subclass of the appropriate `StackedInline` or `TabularInline`
class, and then passing that subclass as the `admin_class` option of
`inline_reverse`.  However, that method no longer works with newer
versions of Django (at least with Django 4.2 and later).

This commit updates the `ReverseInlineModelAdmin` class to determine
`can_delete` in the same way that Django's `InlineModelAdmin` currently
does, and then passes that into the custom formset factory.  In that
way, consumers of this library can simply set the `can_delete` option
directly on their `inline_reverse` specification without subclassing one
of the built-in `InlineModelAdmin` implementations.

Note that this approach was necessary because the custom formset factory
in `django_reverse_admin` lives outside of the `ReverseInlineModelAdmin`
class, and doesn't have access to the parent class' `can_delete`
property and `has_delete_permission` method.

Author: jgregory-fidorum

README.md

@@ -105,29 +105,17 @@ class PersonAdmin(ReverseModelAdmin):
 
 #### Do not allow deletion
 
-django-reverse-admin uses the standard features of in-line forms (Stacked and Tabular). When used in the ReverseAdmin co-text, it releases the option to delete the associated object.
-
-To remove this option (thus making the object unable to be deleted), it is necessary to add the admin_class inheriting from one of the native resources (Stacked and Tabular). Example:
+To prevent deletion of the inlined object, use the `can_delete` option:
 
 ```py
-from .forms import CustomBusinessAddrForm
-
-
-class BarInline(admin.StackedInline):
-    model = Address
-
-    def has_delete_permission(self, request, obj=None):
-        return False
-
-
 class PersonAdmin(ReverseModelAdmin):
     inline_type = 'tabular'
     inline_reverse = [
         'business_addr',
         {
             'field_name': 'home_addr',
             'fields': ('zip_code',),
-            'admin_class': BarInline
+            'can_delete': False,
         }
     ]
 ```

django_reverse_admin/__init__.py

@@ -65,14 +65,15 @@ def reverse_inlineformset_factory(parent_model,
                                   form=ModelForm,
                                   fields=None,
                                   exclude=None,
-                                  formfield_callback=lambda f: f.formfield()):
+                                  formfield_callback=lambda f: f.formfield(),
+                                  **kwargs):
 
     if fields is None and exclude is None:
         related_fields = [f for f in model._meta.get_fields() if
                           (f.one_to_many or f.one_to_one or f.many_to_many) and f.auto_created and not f.concrete]
         fields = [f.name for f in model._meta.get_fields() if f not in
                   related_fields]  # ignoring reverse relations
-    kwargs = {
+    defaults = {
         'form': form,
         'formfield_callback': formfield_callback,
         'formset': ReverseInlineFormSet,
@@ -83,7 +84,8 @@ def reverse_inlineformset_factory(parent_model,
         'exclude': exclude,
         'max_num': 1,
     }
-    FormSet = modelformset_factory(model, **kwargs)
+    defaults.update(**kwargs)
+    FormSet = modelformset_factory(model, **defaults)
     FormSet.parent_fk_name = parent_fk_name
     return FormSet
 
@@ -129,12 +131,14 @@ def get_formset(self, request, obj=None, **kwargs):
         exclude.extend(non_editable_fields)
         # but need exclude to be None if result is an empty list
         exclude = exclude or None
+        can_delete = self.can_delete and self.has_delete_permission(request, obj)
 
         defaults = {
             "form": self.form,
             "fields": fields,
             "exclude": exclude,
             "formfield_callback": partial(self.formfield_for_dbfield, request=request),
+            "can_delete": can_delete,
         }
         kwargs.update(defaults)
         return reverse_inlineformset_factory(self.parent_model,

tests/polls/admin.py

@@ -2,6 +2,7 @@
 from polls.models import Address
 from polls.models import NonInlinePerson
 from polls.models import Person
+from polls.models import PersonNoDeleteAddress
 from polls.models import PersonWithAddressNonId
 from polls.models import PersonWithTwoAddresses
 from polls.models import PhoneNumber
@@ -41,6 +42,15 @@ def get_readonly_fields(self, request, obj=None):
             return self.readonly_fields
 
 
+class PersonNoDeleteAddressAdmin(PersonAdmin):
+    inline_reverse = [
+        ('home_addr', {
+            'fields': ['street', 'city', 'state', 'zipcode'],
+            'can_delete': False,
+        }),
+    ]
+
+
 class PersonWithAddressNonIdAdmin(ReverseModelAdmin):
     list_display = ('name', 'home_addr')
 
@@ -74,6 +84,7 @@ class AddressAdmin(admin.ModelAdmin):
 
 
 admin.site.register(Person, PersonAdmin)
+admin.site.register(PersonNoDeleteAddress, PersonNoDeleteAddressAdmin)
 admin.site.register(PersonWithAddressNonId, PersonWithAddressNonIdAdmin)
 admin.site.register(PersonWithTwoAddresses, PersonWithTwoAddressesAdmin)
 admin.site.register(PhoneNumber, PhoneNumberAdmin)

tests/polls/models.py

@@ -56,6 +56,10 @@ def __str__(self):
         return self.name
 
 
+class PersonNoDeleteAddress(Person):
+    pass
+
+
 class PersonWithAddressNonId(TemporalBase):
     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
     name = models.CharField(max_length=255)