community[patch]: Dynamodb history messages key (#25658)

- **Description:** adding the history_messages_key so you don't have to
use "History" as a key in langchain

libs/community/langchain_community/chat_message_histories/dynamodb.py

@@ -45,6 +45,8 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
             [AWS DynamoDB documentation](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/time-to-live-ttl-how-to.html)
         history_size: Maximum number of messages to store. If None then there is no
             limit. If not None then only the latest `history_size` messages are stored.
+        history_messages_key: Key for the chat history where the messages
+            are stored and updated
     """
 
     def __init__(
@@ -59,6 +61,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         ttl: Optional[int] = None,
         ttl_key_name: str = "expireAt",
         history_size: Optional[int] = None,
+        history_messages_key: Optional[str] = "History",
     ):
         if boto3_session:
             client = boto3_session.resource("dynamodb", endpoint_url=endpoint_url)
@@ -79,6 +82,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         self.ttl = ttl
         self.ttl_key_name = ttl_key_name
         self.history_size = history_size
+        self.history_messages_key = history_messages_key
 
         if kms_key_id:
             try:
@@ -96,7 +100,9 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
 
             actions = AttributeActions(
                 default_action=CryptoAction.DO_NOTHING,
-                attribute_actions={"History": CryptoAction.ENCRYPT_AND_SIGN},
+                attribute_actions={
+                    self.history_messages_key: CryptoAction.ENCRYPT_AND_SIGN
+                },
             )
             aws_kms_cmp = AwsKmsCryptographicMaterialsProvider(key_id=kms_key_id)
             self.table = EncryptedTable(
@@ -126,7 +132,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
                 logger.error(error)
 
         if response and "Item" in response:
-            items = response["Item"]["History"]
+            items = response["Item"][self.history_messages_key]
         else:
             items = []
 
@@ -162,10 +168,16 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
 
                 expireAt = int(time.time()) + self.ttl
                 self.table.put_item(
-                    Item={**self.key, "History": messages, self.ttl_key_name: expireAt}
+                    Item={
+                        **self.key,
+                        self.history_messages_key: messages,
+                        self.ttl_key_name: expireAt,
+                    }
                 )
             else:
-                self.table.put_item(Item={**self.key, "History": messages})
+                self.table.put_item(
+                    Item={**self.key, self.history_messages_key: messages}
+                )
         except ClientError as err:
             logger.error(err)