Cloud SQL is a fully managed relational database service that offers high performance, seamless integration, and impressive scalability and offers database engines such as PostgreSQL. This guide provides a quick overview of how to use Cloud SQL for PostgreSQL to store messages and provide conversation with the PostgresChatMessageHistory class.

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Overview

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Before you begin

In order to use this package, you first need to go through the following steps:
  1. Select or create a Cloud Platform project.
  2. Enable billing for your project.
  3. Enable the Cloud SQL Admin API.
  4. Setup Authentication.
  5. Create a CloudSQL instance
  6. Create a CloudSQL database
  7. Add a user to the database

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Authentication

Authenticate locally to your Google Cloud account using the gcloud auth login command.

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Set Your Google Cloud Project

Set your Google Cloud project ID to leverage Google Cloud resources locally: 
gcloud config set project YOUR-PROJECT-ID
If you don’t know your project ID, try the following:

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Setting up a PostgresChatMessageHistory instance

To use the PostgresChatMessageHistory class, you’ll need to install the @langchain/google-cloud-sql-pg package and then follow the steps bellow. First, you’ll need to log in to your Google Cloud account and set the following environment variables based on your Google Cloud project; these will be defined based on how you want to configure (fromInstance, fromEngine, fromEngineArgs) your PostgresEngine instance: 
PROJECT_ID="your-project-id"
REGION="your-project-region" // example: "us-central1"
INSTANCE_NAME="your-instance"
DB_NAME="your-database-name"
DB_USER="your-database-user"
PASSWORD="your-database-password"

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Setting up an instance

To instantiate a PostgresChatMessageHistory, you’ll first need to create a database connection through the PostgresEngine, then initialize the chat history table and finally call the .initialize() method to instantiate the chat message history. 
import {
  PostgresChatMessageHistory,
  PostgresEngine,
  PostgresEngineArgs,
} from "@langchain/google-cloud-sql-pg";
import * as dotenv from "dotenv";

dotenv.config();

const peArgs: PostgresEngineArgs = {
  user: process.env.DB_USER ?? "",
  password: process.env.PASSWORD ?? "",
};

// PostgresEngine instantiation
const engine: PostgresEngine = await PostgresEngine.fromInstance(
  process.env.PROJECT_ID ?? "",
  process.env.REGION ?? "",
  process.env.INSTANCE_NAME ?? "",
  process.env.DB_NAME ?? "",
  peArgs
);

// Chat history table initialization
await engine.initChatHistoryTable("my_chat_history_table");

// PostgresChatMessageHistory instantiation
const historyInstance: PostgresChatMessageHistory =
  await PostgresChatMessageHistory.initialize(
    engine,
    "test",
    "my_chat_history_table"
  );

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Manage Chat Message History

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Add Messages to the chat history

You can add a message to the chat history by using the addMessage method or you can use the addMessages method to pass an array of messages. 
import { AIMessage, BaseMessage, HumanMessage } from "@langchain/core/messages";

// Add one message
const msg = new HumanMessage("Hi!");
await historyInstance.addMessage(msg);

// Add an array of messages
const msg1: HumanMessage = new HumanMessage("Hi!");
const msg2: AIMessage = new AIMessage("what's up?");
const msg3: HumanMessage = new HumanMessage("How are you?");
const messages: BaseMessage[] = [msg1, msg2, msg3];
await historyInstance.addMessages(messages);

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Get Messages saved on the chat history

const messagesSaved: BaseMessage[] = await historyInstance.getMessages();
console.log(messagesSaved);

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Clear Messages from the chat history

To remove all messages from the chat history, just call the clear method from the PostgresChatMessageHistory class. 
await historyInstance.clear();