feat: enable to use a _resolve_reference method name

Author: Thomas Leonard

README.md

@@ -31,6 +31,8 @@ At the moment it supports:
 
 Each type which is decorated with `@key` or `@extend` is added to the `_Entity` union.
 The [`__resolve_reference` method](https://www.apollographql.com/docs/federation/api/apollo-federation/#__resolvereference) can be defined for each type that is an entity.
+Note that since the notation with double underscores can be problematic in Python for model inheritance this resolver method can also be named `_resolve_reference` (the `__resolve_reference` method will take precedence if both are declared).
+
 This method is called whenever an entity is requested as part of the fulfilling a query plan.
 If not explicitly defined, the default resolver is used.
 The default resolver just creates instance of type with passed fieldset as kwargs, see [`entity.get_entity_query`](graphene_federation/entity.py) for more details

graphene_federation/entity.py

@@ -64,11 +64,9 @@ def resolve_entities(self, info, representations):
                     }
                 model_instance = model(**model_arguments)
 
-                try:
-                    resolver = getattr(model, "_%s__resolve_reference" % model.__name__)
-                except AttributeError:
-                    pass
-                else:
+                resolver = getattr(model, "_%s__resolve_reference" % model.__name__, None) or \
+                    getattr(model, "_resolve_reference", None)
+                if resolver:
                     model_instance = resolver(model_instance, info)
 
                 entities.append(model_instance)