Fix exclude_fields / only_fields

Author: Rami Chowdhury

graphene_pydantic/types.py

@@ -31,16 +31,17 @@ def construct_fields(
     Currently simply fetches all the attributes from the Pydantic model's __fields__. In
     the future we hope to implement field-level overrides that we'll have to merge in.
     """
-    fields = {}
-    if only_fields:
-        fields_to_convert = (
-            (k, v) for k, v in model.__fields__.items() if k in only_fields
-        )
-    elif exclude_fields:
-        fields_to_convert = (
-            (k, v) for k, v in model.__fields__.items() if k not in only_fields
-        )
+    excluded: typing.Tuple[str, ...] = ()
+    if exclude_fields:
+        excluded = exclude_fields
+    elif only_fields:
+        excluded = tuple(k for k in model.__fields__ if k not in only_fields)
 
+    fields_to_convert = (
+        (k, v) for k, v in model.__fields__.items() if k not in excluded
+    )
+
+    fields = {}
     for name, field in fields_to_convert:
         converted = convert_pydantic_field(field, registry)
         registry.register_orm_field(obj_type, name, field)