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*   [Memory](/v0.1/docs/modules/memory/)
*   [Chat Message History](/v0.1/docs/modules/memory/chat_messages/)
*   Custom chat history

Custom chat history
===================

To create your own custom chat history class for a backing store, you can extend the [`BaseListChatMessageHistory`](https://api.js.langchain.com/classes/langchain_core_chat_history.BaseListChatMessageHistory.html) class. This requires you to implement the following methods:

*   `addMessage`, which adds a `BaseMessage` to the store for the current session. This usually involves serializing them into a simple object representation (defined as `StoredMessage` below) that the backing store can handle.
*   `getMessages`, which loads messages for a session and returns them as an array of `BaseMessage`s. For most databases, this involves deserializing stored messages into `BaseMessage`s.

In addition, there are some optional methods that are nice to override:

*   `clear`, which removes all messages from the store.
*   `addMessages`, which will add multiple messages at a time to the current session. This can save round-trips to and from the backing store if many messages are being saved at once. The default implementation will call `addMessage` once per input message.

Here’s an example that stores messages in-memory. For long-term persistence, you should use a real database. You’ll notice we use the `mapChatMessagesToStoredMessages` and `mapStoredMessagesToChatMessages` helper methods for consistent serialization and deserialization:

    import { BaseListChatMessageHistory } from "@langchain/core/chat_history";import {  BaseMessage,  StoredMessage,  mapChatMessagesToStoredMessages,  mapStoredMessagesToChatMessages,} from "@langchain/core/messages";// Not required, but usually chat message histories will handle multiple sessions// for different users, and should take some kind of sessionId as input.export interface CustomChatMessageHistoryInput {  sessionId: string;}export class CustomChatMessageHistory extends BaseListChatMessageHistory {  lc_namespace = ["langchain", "stores", "message"];  sessionId: string;  // Simulate a real database layer. Stores serialized objects.  fakeDatabase: Record<string, StoredMessage[]> = {};  constructor(fields: CustomChatMessageHistoryInput) {    super(fields);    this.sessionId = fields.sessionId;  }  async getMessages(): Promise<BaseMessage[]> {    const messages = this.fakeDatabase[this.sessionId] ?? [];    return mapStoredMessagesToChatMessages(messages);  }  async addMessage(message: BaseMessage): Promise<void> {    if (this.fakeDatabase[this.sessionId] === undefined) {      this.fakeDatabase[this.sessionId] = [];    }    const serializedMessages = mapChatMessagesToStoredMessages([message]);    this.fakeDatabase[this.sessionId].push(serializedMessages[0]);  }  async addMessages(messages: BaseMessage[]): Promise<void> {    if (this.fakeDatabase[this.sessionId] === undefined) {      this.fakeDatabase[this.sessionId] = [];    }    const existingMessages = this.fakeDatabase[this.sessionId];    const serializedMessages = mapChatMessagesToStoredMessages(messages);    this.fakeDatabase[this.sessionId] =      existingMessages.concat(serializedMessages);  }  async clear(): Promise<void> {    delete this.fakeDatabase[this.sessionId];  }}

You can then use this chat history as usual:

    import { AIMessage, HumanMessage } from "@langchain/core/messages";const chatHistory = new CustomChatMessageHistory({ sessionId: "test" });await chatHistory.addMessages([  new HumanMessage("Hello there!"),  new AIMessage("Hello to you too!"),]);await chatHistory.getMessages();

    [  HumanMessage {    lc_serializable: true,    lc_kwargs: { content: "Hello there!", additional_kwargs: {} },    lc_namespace: [ "langchain_core", "messages" ],    content: "Hello there!",    name: undefined,    additional_kwargs: {}  },  AIMessage {    lc_serializable: true,    lc_kwargs: { content: "Hello to you too!", additional_kwargs: {} },    lc_namespace: [ "langchain_core", "messages" ],    content: "Hello to you too!",    name: undefined,    additional_kwargs: {}  }]

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