fix(graph): raise InvalidGQLGenerationError with intermediate_steps

Fixes #178

Author: jordimas

src/langchain_google_spanner/graph_qa.py

@@ -71,6 +71,12 @@ class VerifyGqlOutput(BaseModel):
 INTERMEDIATE_STEPS_KEY = "intermediate_steps"
 
 
+class InvalidGQLGenerationError(ValueError):
+    def __init__(self, message, intermediate_steps=None):
+        self.intermediate_steps = intermediate_steps
+        super().__init__(message)
+
+
 class SpannerGraphQAChain(Chain):
     """Chain for question-answering against a Spanner Graph database by
         generating GQL statements from natural language questions.
@@ -268,7 +274,9 @@ def execute_with_retry(
             finally:
                 retries += 1
 
-        raise ValueError("The generated gql query is invalid")
+        raise InvalidGQLGenerationError(
+            "The generated gql query is invalid", intermediate_steps
+        )
 
     def log_invalid_query(
         self,
@@ -322,7 +330,9 @@ def _call(
                 _run_manager, intermediate_steps, question, verified_gql
             )
             if not final_gql:
-                raise ValueError("No GQL was generated.")
+                raise InvalidGQLGenerationError(
+                    "No GQL was generated.", intermediate_steps
+                )
             _run_manager.on_text("Full Context:", end="\n", verbose=self.verbose)
             _run_manager.on_text(
                 str(context), color="green", end="\n", verbose=self.verbose