*   [](/v0.2/)
*   [How-to guides](/v0.2/docs/how_to/)
*   How to handle multiple retrievers

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How to handle multiple retrievers
=================================

Prerequisites

This guide assumes familiarity with the following:

*   [Query analysis](/v0.2/docs/tutorials/query_analysis)

Sometimes, a query analysis technique may allow for selection of which retriever to use. To use this, you will need to add some logic to select the retriever to do. We will show a simple example (using mock data) of how to do that.

Setup[​](#setup "Direct link to Setup")
---------------------------------------

### Install dependencies[​](#install-dependencies "Direct link to Install dependencies")

tip

See [this section for general instructions on installing integration packages](/v0.2/docs/how_to/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/community @langchain/openai zod chromadb

    yarn add @langchain/community @langchain/openai zod chromadb

    pnpm add @langchain/community @langchain/openai zod chromadb

### Set environment variables[​](#set-environment-variables "Direct link to Set environment variables")

    OPENAI_API_KEY=your-api-key# Optional, use LangSmith for best-in-class observabilityLANGSMITH_API_KEY=your-api-keyLANGCHAIN_TRACING_V2=true

### Create Index[​](#create-index "Direct link to Create Index")

We will create a vectorstore over fake information.

    import { Chroma } from "@langchain/community/vectorstores/chroma";import { OpenAIEmbeddings } from "@langchain/openai";import "chromadb";const texts = ["Harrison worked at Kensho"];const embeddings = new OpenAIEmbeddings({ model: "text-embedding-3-small" });const vectorstore = await Chroma.fromTexts(texts, {}, embeddings, {  collectionName: "harrison",});const retrieverHarrison = vectorstore.asRetriever(1);const texts = ["Ankush worked at Facebook"];const embeddings = new OpenAIEmbeddings({ model: "text-embedding-3-small" });const vectorstore = await Chroma.fromTexts(texts, {}, embeddings, {  collectionName: "ankush",});const retrieverAnkush = vectorstore.asRetriever(1);

Query analysis[​](#query-analysis "Direct link to Query analysis")
------------------------------------------------------------------

We will use function calling to structure the output. We will let it return multiple queries.

    import { z } from "zod";const searchSchema = z.object({  query: z.string().describe("Query to look up"),  person: z    .string()    .describe(      "Person to look things up for. Should be `HARRISON` or `ANKUSH`."    ),});

### Pick your chat model:

*   OpenAI
*   Anthropic
*   FireworksAI
*   MistralAI
*   Groq
*   VertexAI

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/openai 

    yarn add @langchain/openai 

    pnpm add @langchain/openai 

#### Add environment variables

    OPENAI_API_KEY=your-api-key

#### Instantiate the model

    import { ChatOpenAI } from "@langchain/openai";const llm = new ChatOpenAI({  model: "gpt-3.5-turbo",  temperature: 0});

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/anthropic 

    yarn add @langchain/anthropic 

    pnpm add @langchain/anthropic 

#### Add environment variables

    ANTHROPIC_API_KEY=your-api-key

#### Instantiate the model

    import { ChatAnthropic } from "@langchain/anthropic";const llm = new ChatAnthropic({  model: "claude-3-sonnet-20240229",  temperature: 0});

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/community 

    yarn add @langchain/community 

    pnpm add @langchain/community 

#### Add environment variables

    FIREWORKS_API_KEY=your-api-key

#### Instantiate the model

    import { ChatFireworks } from "@langchain/community/chat_models/fireworks";const llm = new ChatFireworks({  model: "accounts/fireworks/models/firefunction-v1",  temperature: 0});

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/mistralai 

    yarn add @langchain/mistralai 

    pnpm add @langchain/mistralai 

#### Add environment variables

    MISTRAL_API_KEY=your-api-key

#### Instantiate the model

    import { ChatMistralAI } from "@langchain/mistralai";const llm = new ChatMistralAI({  model: "mistral-large-latest",  temperature: 0});

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/groq 

    yarn add @langchain/groq 

    pnpm add @langchain/groq 

#### Add environment variables

    GROQ_API_KEY=your-api-key

#### Instantiate the model

    import { ChatGroq } from "@langchain/groq";const llm = new ChatGroq({  model: "mixtral-8x7b-32768",  temperature: 0});

#### Install dependencies

tip

See [this section for general instructions on installing integration packages](/docs/get_started/installation#installing-integration-packages).

*   npm
*   yarn
*   pnpm

    npm i @langchain/google-vertexai 

    yarn add @langchain/google-vertexai 

    pnpm add @langchain/google-vertexai 

#### Add environment variables

    GOOGLE_APPLICATION_CREDENTIALS=credentials.json

#### Instantiate the model

    import { ChatVertexAI } from "@langchain/google-vertexai";const llm = new ChatVertexAI({  model: "gemini-1.5-pro",  temperature: 0});

    import { ChatPromptTemplate } from "@langchain/core/prompts";import {  RunnableSequence,  RunnablePassthrough,} from "@langchain/core/runnables";const system = `You have the ability to issue search queries to get information to help answer user information.`;const prompt = ChatPromptTemplate.fromMessages([  ["system", system],  ["human", "{question}"],]);const llmWithTools = llm.withStructuredOutput(searchSchema, {  name: "Search",});const queryAnalyzer = RunnableSequence.from([  {    question: new RunnablePassthrough(),  },  prompt,  llmWithTools,]);

We can see that this allows for routing between retrievers

    await queryAnalyzer.invoke("where did Harrison Work");

    { query: "workplace of Harrison", person: "HARRISON" }

    await queryAnalyzer.invoke("where did ankush Work");

    { query: "Workplace of Ankush", person: "ANKUSH" }

Retrieval with query analysis[​](#retrieval-with-query-analysis "Direct link to Retrieval with query analysis")
---------------------------------------------------------------------------------------------------------------

So how would we include this in a chain? We just need some simple logic to select the retriever and pass in the search query

    const retrievers = {  HARRISON: retrieverHarrison,  ANKUSH: retrieverAnkush,};

    import { RunnableConfig, RunnableLambda } from "@langchain/core/runnables";const chain = async (question: string, config?: RunnableConfig) => {  const response = await queryAnalyzer.invoke(question, config);  const retriever = retrievers[response.person];  return retriever.invoke(response.query, config);};const customChain = new RunnableLambda({ func: chain });

    await customChain.invoke("where did Harrison Work");

    [ Document { pageContent: "Harrison worked at Kensho", metadata: {} } ]

    await customChain.invoke("where did ankush Work");

    [ Document { pageContent: "Ankush worked at Facebook", metadata: {} } ]

Next steps[​](#next-steps "Direct link to Next steps")
------------------------------------------------------

You’ve now learned some techniques for handling multiple retrievers in a query analysis system.

Next, check out some of the other query analysis guides in this section, like [how to deal with cases where no query is generated](/v0.2/docs/how_to/query_no_queries).

* * *

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How to handle multiple queries

](/v0.2/docs/how_to/query_multiple_queries)[

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How to handle cases where no queries are generated

](/v0.2/docs/how_to/query_no_queries)

*   [Setup](#setup)
    *   [Install dependencies](#install-dependencies)
    *   [Set environment variables](#set-environment-variables)
    *   [Create Index](#create-index)
*   [Query analysis](#query-analysis)
*   [Retrieval with query analysis](#retrieval-with-query-analysis)
*   [Next steps](#next-steps)