Minor fix in @keys

Author: arun-sureshkumar

examples/inaccessible.py

@@ -1,10 +1,11 @@
 import graphene
 
-from graphene_federation import inaccessible, shareable, extend, requires, external, provides
+from graphene_federation import inaccessible, external, provides, key
 
 from graphene_federation import build_schema
 
 
+@key(fields="x")
 class Position(graphene.ObjectType):
     x = graphene.Int(required=True)
     y = external(graphene.Int(required=True))

graphene_federation/entity.py

@@ -87,19 +87,9 @@ def key(fields: str) -> Callable:
     """
     Take as input a field that should be used as key for that entity.
     See specification: https://www.apollographql.com/docs/federation/federation-spec/#key
-
-    If the input contains a space it means it's a [compound primary key](https://www.apollographql.com/docs/federation/entities/#defining-a-compound-primary-key)
-    which is not yet supported.
     """
-    if " " in fields:
-        raise NotImplementedError("Compound primary keys are not supported.")
 
     def decorator(Type):
-        # Check the provided fields actually exist on the Type.
-        assert (
-                fields in Type._meta.fields
-        ), f'Field "{fields}" does not exist on type "{Type._meta.name}"'
-
         keys = getattr(Type, "_keys", [])
         keys.append(fields)
         setattr(Type, "_keys", keys)