fix: Fix QueryOptions not applied to similarity search bug (#185)

* fix: Fix QueryOptions not applied to similarity search bug

* syntax

Author: duwenxin99

src/langchain_google_cloud_sql_pg/engine.py

@@ -327,7 +327,7 @@ async def _aexecute(self, query: str, params: Optional[dict] = None) -> None:
             await conn.commit()
 
     async def _aexecute_outside_tx(self, query: str) -> None:
-        """Execute a SQL query."""
+        """Execute a SQL query in a new transaction."""
         async with self._engine.connect() as conn:
             await conn.execute(text("COMMIT"))
             await conn.execute(text(query))
@@ -343,6 +343,18 @@ async def _afetch(
 
         return result_fetch
 
+    async def _afetch_with_query_options(
+        self, query: str, query_options: str
+    ) -> Sequence[RowMapping]:
+        """Set temporary database flags and fetch results from a SQL query."""
+        async with self._engine.connect() as conn:
+            await conn.execute(text(query_options))
+            result = await conn.execute(text(query))
+            result_map = result.mappings()
+            result_fetch = result_map.fetchall()
+
+        return result_fetch
+
     def _execute(self, query: str, params: Optional[dict] = None) -> None:
         """Execute a SQL query."""
         return self._run_as_sync(self._aexecute(query, params))

src/langchain_google_cloud_sql_pg/vectorstore.py

@@ -599,10 +599,12 @@ async def __query_collection(
         filter = f"WHERE {filter}" if filter else ""
         stmt = f"SELECT *, {search_function}({self.embedding_column}, '{embedding}') as distance FROM \"{self.table_name}\" {filter} ORDER BY {self.embedding_column} {operator} '{embedding}' LIMIT {k};"
         if self.index_query_options:
-            await self.engine._aexecute(
-                f"SET LOCAL {self.index_query_options.to_string()};"
+            query_options_stmt = f"SET LOCAL {self.index_query_options.to_string()};"
+            results = await self.engine._afetch_with_query_options(
+                stmt, query_options_stmt
             )
-        results = await self.engine._afetch(stmt)
+        else:
+            results = await self.engine._afetch(stmt)
         return results
 
     def similarity_search(