Fix _id handling for LLM pipeline generation

Author: NoahStapp

libs/langchain-mongodb/langchain_mongodb/agent_toolkit/database.py

@@ -341,10 +341,15 @@ def _handle_object_id(match: Any) -> str:
                 raise ValueError("ObjectId must contain a value.")
             return f"ObjectId('{oid_str}')"
 
+        def _handle_id_key(match: Any) -> str:
+            return f'"{match.group(1)}"'
+
         patterns = [
             (r'ISODate\(\s*["\']([^"\']*)["\']\s*\)', _handle_iso_date),
             (r'new\s+Date\(\s*["\']([^"\']*)["\']\s*\)', _handle_new_date),
             (r'ObjectId\(\s*["\']([^"\']*)["\']\s*\)', _handle_object_id),
+            (r'ObjectId\(\s*["\']([^"\']*)["\']\s*\)', _handle_object_id),
+            (r'(?<!["\'])\b(_id)\b(?!["\'])', _handle_id_key),
         ]
 
         for pattern, replacer in patterns: