work hard on this

aircox/admin/mixins.py

@@ -0,0 +1,42 @@
+class UnrelatedInlineMixin:
+    """
+    Inline class that can be included in an admin change view whose model
+    is not directly related to inline's model.
+    """
+    view_model = None
+    parent_model = None
+    parent_fk = ''
+
+    def __init__(self, parent_model, admin_site):
+        self.view_model = parent_model
+        super().__init__(self.parent_model, admin_site)
+
+    def get_parent(self, view_obj):
+        """ Get formset's instance from `obj` of AdminSite's change form. """
+        field = self.parent_model._meta.get_field(self.parent_fk).remote_field
+        return getattr(view_obj, field.name, None)
+
+    def save_parent(self, parent, view_obj):
+        """ Save formset's instance. """
+        setattr(parent, self.parent_fk, view_obj)
+        parent.save()
+        return parent
+
+    def get_formset(self, request, obj):
+        ParentFormSet = super().get_formset(request, obj)
+        inline = self
+        class FormSet(ParentFormSet):
+            view_obj = None
+
+            def __init__(self, *args, instance=None, **kwargs):
+                self.view_obj = instance
+                instance = inline.get_parent(instance)
+                self.instance = instance
+                super().__init__(*args, instance=instance, **kwargs)
+
+            def save(self):
+                inline.save_parent(self.instance, self.view_obj)
+                return super().save()
+        return FormSet
+
+