Improvements for model metadata introspection (#4585)

- Will improve API permissions checks
- Will improve API metadata checks
- Fixes missing model information on metadata options endpoints

Ref: https://github.com/inventree/InvenTree/pull/4579

InvenTree/InvenTree/api.py

@@ -361,6 +361,10 @@ class MetadataView(RetrieveUpdateAPI):
 
         return model
 
+    def get_permission_model(self):
+        """Return the 'permission' model associated with this view"""
+        return self.get_model_type()
+
     def get_queryset(self):
         """Return the queryset for this endpoint"""
         return self.get_model_type().objects.all()

InvenTree/InvenTree/metadata.py

@@ -7,6 +7,7 @@ from rest_framework.fields import empty
 from rest_framework.metadata import SimpleMetadata
 from rest_framework.utils import model_meta
 
+import InvenTree.permissions
 import users.models
 from InvenTree.helpers import str2bool
 
@@ -58,7 +59,7 @@ class InvenTreeMetadata(SimpleMetadata):
 
         try:
             # Extract the model name associated with the view
-            self.model = view.serializer_class.Meta.model
+            self.model = InvenTree.permissions.get_model_for_view(view)
 
             # Construct the 'table name' from the model
             app_label = self.model._meta.app_label

InvenTree/InvenTree/permissions.py

@@ -7,6 +7,21 @@ from rest_framework import permissions
 import users.models
 
 
+def get_model_for_view(view, raise_error=True):
+    """Attempt to introspect the 'model' type for an API view"""
+
+    if hasattr(view, 'get_permission_model'):
+        return view.get_permission_model()
+
+    if hasattr(view, 'serializer_class'):
+        return view.serializer_class.Meta.model
+
+    if hasattr(view, 'get_serializer_class'):
+        return view.get_serializr_class().Meta.model
+
+    raise AttributeError(f"Serializer class not specified for {view.__class__}")
+
+
 class RolePermission(permissions.BasePermission):
     """Role mixin for API endpoints, allowing us to specify the user "role" which is required for certain operations.
 
@@ -55,7 +70,7 @@ class RolePermission(permissions.BasePermission):
 
         try:
             # Extract the model name associated with this request
-            model = view.serializer_class.Meta.model
+            model = get_model_for_view(view)
 
             app_label = model._meta.app_label
             model_name = model._meta.model_name