Store the incoming text at /converse endpoint in the form of ChatMessage object

[skks1212]

Store the incoming text at /converse endpoint to create a new ChatMessage object (model is already defined). Now create a new serializer called ChatDetailSerializer that gets used only while retrieving a chat (through /chats/<external_id>) that adds a chats field which is a reference to ChatMessageSerializer (which you also have to create) that is a model serializer for ChatMessage.

Now once this is done, update the /converse endpoint such that the previous messages also get chained through langchain.