File System Store

Compatibility

Only available on Node.js.

This example demonstrates how to setup chat history storage using the LocalFileStore KV store integration.

Usage

info

The path passed to the .fromPath must be a directory, not a file.

The LocalFileStore is a wrapper around the fs module for storing data as key-value pairs. Each key value pair has its own file nested inside the directory passed to the .fromPath method. The file name is the key and inside contains the value of the key.

import fs from "fs";
import { LocalFileStore } from "langchain/storage/file_system";
import { AIMessage, HumanMessage } from "@langchain/core/messages";

// Instantiate the store using the `fromPath` method.
const store = await LocalFileStore.fromPath("./messages");
// Define our encoder/decoder for converting between strings and Uint8Arrays
const encoder = new TextEncoder();
const decoder = new TextDecoder();
/**
 * Here you would define your LLM and chat chain, call
 * the LLM and eventually get a list of messages.
 * For this example, we'll assume we already have a list.
 */
const messages = Array.from({ length: 5 }).map((_, index) => {
  if (index % 2 === 0) {
    return new AIMessage("ai stuff...");
  }
  return new HumanMessage("human stuff...");
});
// Set your messages in the store
// The key will be prefixed with `message:id:` and end
// with the index.
await store.mset(
  messages.map((message, index) => [
    `message:id:${index}`,
    encoder.encode(JSON.stringify(message)),
  ])
);
// Now you can get your messages from the store
const retrievedMessages = await store.mget(["message:id:0", "message:id:1"]);
// Make sure to decode the values
console.log(retrievedMessages.map((v) => decoder.decode(v)));
/**
[
  '{"id":["langchain","AIMessage"],"kwargs":{"content":"ai stuff..."}}',
  '{"id":["langchain","HumanMessage"],"kwargs":{"content":"human stuff..."}}'
]
 */
// Or, if you want to get back all the keys you can call
// the `yieldKeys` method.
// Optionally, you can pass a key prefix to only get back
// keys which match that prefix.
const yieldedKeys = [];
for await (const key of store.yieldKeys("message:id:")) {
  yieldedKeys.push(key);
}
// The keys are not encoded, so no decoding is necessary
console.log(yieldedKeys);
/**
[
  'message:id:2',
  'message:id:1',
  'message:id:3',
  'message:id:0',
  'message:id:4'
]
 */
// Finally, let's delete the keys from the store
// and delete the file.
await store.mdelete(yieldedKeys);
await fs.promises.rm("./messages", { recursive: true, force: true });

API Reference:

• LocalFileStore from langchain/storage/file_system
• AIMessage from @langchain/core/messages
• HumanMessage from @langchain/core/messages