IMPROVEMENT self-query template (#13305)

- [ ]
https://github.com/langchain-ai/langchain/pull/12694#discussion_r1391334719
-> keep date
- [x]
https://github.com/langchain-ai/langchain/pull/12694#discussion_r1391336586

libs/langchain/langchain/chains/query_constructor/parser.py

@@ -1,4 +1,5 @@
 import datetime
+import warnings
 from typing import Any, Literal, Optional, Sequence, Union
 
 from typing_extensions import TypedDict
@@ -55,6 +56,8 @@ GRAMMAR = r"""
 
 
 class ISO8601Date(TypedDict):
+    """A date in ISO 8601 format (YYYY-MM-DD)."""
+
     date: str
     type: Literal["date"]
 
@@ -140,11 +143,11 @@ class QueryTransformer(Transformer):
         item = str(item).strip("\"'")
         try:
             datetime.datetime.strptime(item, "%Y-%m-%d")
-        except ValueError as e:
-            raise ValueError(
+        except ValueError:
+            warnings.warn(
                 "Dates are expected to be provided in ISO 8601 date format "
                 "(YYYY-MM-DD)."
-            ) from e
+            )
         return {"date": item, "type": "date"}
 
     def string(self, item: Any) -> str: