chore: add missing return type hints

src/langchain_google_cloud_sql_mysql/engine.py

@@ -15,12 +15,14 @@
 # TODO: Remove below import when minimum supported Python version is 3.10
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Dict, List, Optional
+from typing import TYPE_CHECKING, Dict, List, Optional, Sequence
 
 import google.auth
 import google.auth.transport.requests
 import requests
 import sqlalchemy
+from sqlalchemy.engine.row import RowMapping
+
 from google.cloud.sql.connector import Connector, RefreshStrategy
 
 from .version import __version__
@@ -235,15 +237,17 @@ def _execute_outside_tx(self, query: str, params: Optional[dict] = None) -> None
             conn = conn.execution_options(isolation_level="AUTOCOMMIT")
             conn.execute(sqlalchemy.text(query), params)
 
-    def _fetch(self, query: str, params: Optional[dict] = None):
+    def _fetch(self, query: str, params: Optional[dict] = None) -> Sequence[RowMapping]:
         """Fetch results from a SQL query."""
         with self.engine.connect() as conn:
             result = conn.execute(sqlalchemy.text(query), params)
             result_map = result.mappings()
             result_fetch = result_map.fetchall()
             return result_fetch
 
-    def _fetch_rows(self, query: str, params: Optional[dict] = None):
+    def _fetch_rows(
+        self, query: str, params: Optional[dict] = None
+    ) -> Sequence[RowMapping]:
         """Fetch results from a SQL query as rows."""
         with self.engine.connect() as conn:
             result = conn.execute(sqlalchemy.text(query), params)

src/langchain_google_cloud_sql_mysql/vectorstore.py

@@ -234,7 +234,7 @@ def delete(
         self.engine._execute(query)
         return True
 
-    def apply_vector_index(self, vector_index: VectorIndex):
+    def apply_vector_index(self, vector_index: VectorIndex) -> None:
         # Construct the default index name
         if not vector_index.name:
             vector_index.name = f"{self.table_name}_{DEFAULT_INDEX_NAME_SUFFIX}"
@@ -243,7 +243,7 @@ def apply_vector_index(self, vector_index: VectorIndex):
         # After applying an index to the table, set the query option search type to be ANN
         self.query_options.search_type = SearchType.ANN
 
-    def alter_vector_index(self, vector_index: VectorIndex):
+    def alter_vector_index(self, vector_index: VectorIndex) -> None:
         existing_index_name = self._get_vector_index_name()
         if not existing_index_name:
             raise ValueError("No existing vector index found.")
@@ -258,7 +258,9 @@ def alter_vector_index(self, vector_index: VectorIndex):
         )
         self.__exec_apply_vector_index(query_template, vector_index)
 
-    def __exec_apply_vector_index(self, query_template: str, vector_index: VectorIndex):
+    def __exec_apply_vector_index(
+        self, query_template: str, vector_index: VectorIndex
+    ) -> None:
         index_options = []
         if vector_index.index_type:
             index_options.append(f"index_type={vector_index.index_type.value}")
@@ -275,15 +277,15 @@ def __exec_apply_vector_index(self, query_template: str, vector_index: VectorInd
         stmt = query_template.format(index_options_query)
         self.engine._execute_outside_tx(stmt)
 
-    def _get_vector_index_name(self):
+    def _get_vector_index_name(self) -> Optional[str]:
         query = f"SELECT index_name FROM mysql.vector_indexes WHERE table_name='{self.db_name}.{self.table_name}';"
         result = self.engine._fetch(query)
         if result:
             return result[0]["index_name"]
         else:
             return None
 
-    def drop_vector_index(self):
+    def drop_vector_index(self) -> Optional[str]:
         existing_index_name = self._get_vector_index_name()
         if existing_index_name:
             self.engine._execute_outside_tx(