community[patch]: avoid executing `toolkit.get_context()` when not necessary (#19762)

If `prompt` is passed into `create_sql_agent()`, then
`toolkit.get_context()` shouldn't be executed against the database
unless relevant prompt variables (`table_info` or `table_names`) are
present .

libs/community/langchain_community/agent_toolkits/sql/base.py

@@ -150,17 +150,18 @@ def create_sql_agent(
             prompt = prompt.partial(top_k=str(top_k))
         if "dialect" in prompt.input_variables:
             prompt = prompt.partial(dialect=toolkit.dialect)
-        db_context = toolkit.get_context()
-        if "table_info" in prompt.input_variables:
-            prompt = prompt.partial(table_info=db_context["table_info"])
-            tools = [
-                tool for tool in tools if not isinstance(tool, InfoSQLDatabaseTool)
-            ]
-        if "table_names" in prompt.input_variables:
-            prompt = prompt.partial(table_names=db_context["table_names"])
-            tools = [
-                tool for tool in tools if not isinstance(tool, ListSQLDatabaseTool)
-            ]
+        if any(key in prompt.input_variables for key in ["table_info", "table_names"]):
+            db_context = toolkit.get_context()
+            if "table_info" in prompt.input_variables:
+                prompt = prompt.partial(table_info=db_context["table_info"])
+                tools = [
+                    tool for tool in tools if not isinstance(tool, InfoSQLDatabaseTool)
+                ]
+            if "table_names" in prompt.input_variables:
+                prompt = prompt.partial(table_names=db_context["table_names"])
+                tools = [
+                    tool for tool in tools if not isinstance(tool, ListSQLDatabaseTool)
+                ]
 
     if agent_type == AgentType.ZERO_SHOT_REACT_DESCRIPTION:
         if prompt is None: