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*   Stores

On this page

Stores
======

Storing data in key value format is quick and efficient, and can be a powerful tool for LLM applications. The `BaseStore` class provides a simple interface for getting, setting, deleting and iterating over lists of key value pairs.

The public API of `BaseStore` in LangChain JS offers four main methods:

    abstract mget(keys: K[]): Promise<(V | undefined)[]>;abstract mset(keyValuePairs: [K, V][]): Promise<void>;abstract mdelete(keys: K[]): Promise<void>;abstract yieldKeys(prefix?: string): AsyncGenerator<K | string>;

The `m` prefix stands for multiple, and indicates that these methods can be used to get, set and delete multiple key value pairs at once. The `yieldKeys` method is a generator function that can be used to iterate over all keys in the store, or all keys with a given prefix.

It's that simple!

So far LangChain.js has two base integrations for `BaseStore`:

*   [`InMemoryStore`](/v0.2/docs/integrations/stores/in_memory)
*   [`LocalFileStore`](/v0.2/docs/integrations/stores/file_system) (Node.js only)

Use Cases[​](#use-cases "Direct link to Use Cases")
---------------------------------------------------

### Chat history[​](#chat-history "Direct link to Chat history")

If you're building web apps with chat, the `BaseStore` family of integrations can come in very handy for storing and retrieving chat history.

### Caching[​](#caching "Direct link to Caching")

The `BaseStore` family can be a useful alternative to our other caching integrations. For example the [`LocalFileStore`](/v0.2/docs/integrations/stores/file_system) allows for persisting data through the file system. It also is incredibly fast, so your users will be able to access cached data in a snap.

See the individual sections for deeper dives on specific storage providers.

Reading Data[​](#reading-data "Direct link to Reading Data")
------------------------------------------------------------

### In Memory[​](#in-memory "Direct link to In Memory")

Reading data is simple with KV stores. Below is an example using the [`InMemoryStore`](/v0.2/docs/integrations/stores/in_memory) and the `.mget()` method. We'll also set our generic value type to `string` so we can have type safety setting our strings.

Import the [`InMemoryStore`](/v0.2/docs/integrations/stores/in_memory) class.

    import { InMemoryStore } from "langchain/storage/in_memory";

Instantiate a new instance and pass `string` as our generic for the value type.

    const store = new InMemoryStore<string>();

Next we can call `.mset()` to write multiple values at once.

    const data: [string, string][] = [  ["key1", "value1"],  ["key2", "value2"],];await store.mset(data);

Finally, call the `.mget()` method to retrieve the values from our store.

    const data = await store.mget(["key1", "key2"]);console.log(data);/** * ["value1", "value2"] */

### File System[​](#file-system "Direct link to File System")

When using the file system integration we need to instantiate via the `fromPath` method. This is required because it needs to preform checks to ensure the directory exists and is readable/writable. You also must use a directory when using [`LocalFileStore`](/v0.2/docs/integrations/stores/file_system) because each entry is stored as a unique file in the directory.

    import { LocalFileStore } from "langchain/storage/file_system";

    const pathToStore = "./my-store-directory";const store = await LocalFileStore.fromPath(pathToStore);

To do this we can define an encoder for initially setting our data, and a decoder for when we retrieve data.

    const encoder = new TextEncoder();const decoder = new TextDecoder();

    const data: [string, Uint8Array][] = [  ["key1", encoder.encode(new Date().toDateString())],  ["key2", encoder.encode(new Date().toDateString())],];await store.mset(data);

    const data = await store.mget(["key1", "key2"]);console.log(data.map((v) => decoder.decode(v)));/** * [ 'Wed Jan 03 2024', 'Wed Jan 03 2024' ] */

Writing Data[​](#writing-data "Direct link to Writing Data")
------------------------------------------------------------

### In Memory[​](#in-memory-1 "Direct link to In Memory")

Writing data is simple with KV stores. Below is an example using the [`InMemoryStore`](/v0.2/docs/integrations/stores/in_memory) and the `.mset()` method. We'll also set our generic value type to `Date` so we can have type safety setting our dates.

Import the [`InMemoryStore`](/v0.2/docs/integrations/stores/in_memory) class.

    import { InMemoryStore } from "langchain/storage/in_memory";

Instantiate a new instance and pass `Date` as our generic for the value type.

    const store = new InMemoryStore<Date>();

Finally we can call `.mset()` to write multiple values at once.

    const data: [string, Date][] = [  ["date1", new Date()],  ["date2", new Date()],];await store.mset(data);

### File System[​](#file-system-1 "Direct link to File System")

When using the file system integration we need to instantiate via the `fromPath` method. This is required because it needs to preform checks to ensure the directory exists and is readable/writable. You also must use a directory when using [`LocalFileStore`](/v0.2/docs/integrations/stores/file_system) because each entry is stored as a unique file in the directory.

    import { LocalFileStore } from "langchain/storage/file_system";

    const pathToStore = "./my-store-directory";const store = await LocalFileStore.fromPath(pathToStore);

When defining our data we must convert the values to `Uint8Array` because the file system integration only supports binary data.

To do this we can define an encoder for initially setting our data, and a decoder for when we retrieve data.

    const encoder = new TextEncoder();const decoder = new TextDecoder();

    const data: [string, Uint8Array][] = [  ["key1", encoder.encode(new Date().toDateString())],  ["key2", encoder.encode(new Date().toDateString())],];await store.mset(data);

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*   [Use Cases](#use-cases)
    *   [Chat history](#chat-history)
    *   [Caching](#caching)
*   [Reading Data](#reading-data)
    *   [In Memory](#in-memory)
    *   [File System](#file-system)
*   [Writing Data](#writing-data)
    *   [In Memory](#in-memory-1)
    *   [File System](#file-system-1)

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