diff --git a/graph.py b/graph.py
index b0ee020..fd98ec9 100644
--- a/graph.py
+++ b/graph.py
@@ -9,7 +9,7 @@
 
 import typing
 
-@dataclass
+@dataclass(frozen=True)
 class Node:
     table:str
     primary_key:typing.Any