InMemoryStore

This will help you get started with InMemoryStore. For detailed documentation of all InMemoryStore features and configurations head to the API reference.

The InMemoryStore allows for a generic type to be assigned to the values in the store. We’ll assign type BaseMessage as the type of our values, keeping with the theme of a chat history store.

Overview

Integration details

Class	Package	Local	PY support	Package downloads	Package latest
InMemoryStore	@langchain/core	✅	✅

Setup

Installation

The LangChain InMemoryStore integration lives in the @langchain/core package:

tip

See this section for general instructions on installing integration packages.

npm

npm i @langchain/core

yarn

yarn add @langchain/core

pnpm

pnpm add @langchain/core

Instantiation

Now we can instantiate our byte store:

import { InMemoryStore } from "@langchain/core/stores";
import { BaseMessage } from "@langchain/core/messages";

const kvStore = new InMemoryStore<BaseMessage>();

Usage

You can set data under keys like this using the mset method:

import { AIMessage, HumanMessage } from "@langchain/core/messages";

await kvStore.mset([
  ["key1", new HumanMessage("value1")],
  ["key2", new AIMessage("value2")],
]);

await kvStore.mget(["key1", "key2"]);

[
  HumanMessage {
    "content": "value1",
    "additional_kwargs": {},
    "response_metadata": {}
  },
  AIMessage {
    "content": "value2",
    "additional_kwargs": {},
    "response_metadata": {},
    "tool_calls": [],
    "invalid_tool_calls": []
  }
]

And you can delete data using the mdelete method:

await kvStore.mdelete(["key1", "key2"]);

await kvStore.mget(["key1", "key2"]);

[ undefined, undefined ]

Yielding values

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.

import { InMemoryStore } from "@langchain/core/stores";
import { AIMessage, BaseMessage, HumanMessage } from "@langchain/core/messages";

const kvStoreForYield = new InMemoryStore<BaseMessage>();

// Add some data to the store
await kvStoreForYield.mset([
  ["message:id:key1", new HumanMessage("value1")],
  ["message:id:key2", new AIMessage("value2")],
]);

const yieldedKeys = [];
for await (const key of kvStoreForYield.yieldKeys("message:id:")) {
  yieldedKeys.push(key);
}

console.log(yieldedKeys);

[ 'message:id:key1', 'message:id:key2' ]

API reference

For detailed documentation of all InMemoryStore features and configurations, head to the API reference

Related

• Key-value store conceptual guide