⨯ Error: Chains used in SimpleSequentialChain should all have one output, got 2 for retrieval_qa.

[Elindo586]

Why would I be getting this error and how can I fix it?

⨯ Error: Chains used in SimpleSequentialChain should all have one output, got 2 for retrieval_qa.
    at SimpleSequentialChain._validateChains (file:///C:/Users/Edgar/Desktop/Stuff/Acode/nextprojectd/node_modules/langchain/dist/chains/sequential_chain.js:230:23)
    at new SimpleSequentialChain (file:///C:/Users/Edgar/Desktop/Stuff/Acode/nextprojectd/node_modules/langchain/dist/chains/sequential_chain.js:221:14)
    at useStore (webpack-internal:///(api)/./pages/api/usestore.js:83:24) {
  page: '/api/usestore'

Code is here:

import { TextLoader } from "langchain/document_loaders/fs/text";
import { CharacterTextSplitter } from "langchain/text_splitter";
import { OpenAIEmbeddings } from "langchain/embeddings/openai";
import { FaissStore } from "langchain/vectorstores/faiss";

import { OpenAI } from "langchain/llms/openai";
import { PromptTemplate } from "langchain/prompts";
import {
  SimpleSequentialChain,
  LLMChain,
  RetrievalQAChain,
  loadQAStuffChain,
} from "langchain/chains";

let loader;
let docs;
let splitter;
let documents;
let embeddings1;
let vectorstore;

let template1;
let reviewPromptTemplate1;
let reviewChain1;

let model;
let embeddings;
let vectoreStore;
let vectorChain;
let overallChain;

const useStore = async (req, res) => {
  if (req.method === "POST") {
    loader = new TextLoader("./documents/restaurant.txt");
    docs = await loader.load();
    splitter = new CharacterTextSplitter({
      chunkSize: 200,
      chunkOverlap: 50,
    });
    documents = await splitter.splitDocuments(docs);
    embeddings1 = new OpenAIEmbeddings();
    vectorstore = await FaissStore.fromDocuments(documents, embeddings1);
    await vectorstore.save("./");

    const message = req.body.newText;
    const firstOne = req.body.firstMsg;

    console.log(message);
    if (firstOne) {
      model = new OpenAI({
        openAIApiKey: process.env.OPENAI_API_KEY,
        temperature: 0,
      });
      template1 = `
    Be very funny when answering questions. You are a helpful bot that creates a 'thank you' response text.
    If customers are unsatisfied, offer them a real world assistant to talk to.
    You will get a sentiment and subject as input and evaluate.
    
    text: {input}
    `;
      reviewPromptTemplate1 = new PromptTemplate({
        template: template1,
        inputVariables: ["input"],
      });

      reviewChain1 = new LLMChain({ model, prompt: reviewPromptTemplate1 });

      embeddings = new OpenAIEmbeddings();
      vectoreStore = await FaissStore.load("./", embeddings);

      vectorChain = new RetrievalQAChain({
        combineDocumentsChain: loadQAStuffChain(model),
        retriever: vectoreStore.asRetriever(),
        returnSourceDocuments: true,
      });
    }
    overallChain = new SimpleSequentialChain({
      chains: [reviewChain1, vectorChain],
      verbose: true,
    });

    const result = await overallChain.run({
      input: message,
    });

    console.log(result.text);

    return res.status(200).json({ output: result });
  } else {
    res.status(405).json({ say: "Only POST is allowed" });
  }
};
export default useStore;

[dosubot[bot]]

🤖

Hello,

The error you're encountering is due to the SimpleSequentialChain expecting all chains used within it to have only one output. However, your RetrievalQAChain (used as vectorChain) is producing more than one output because of the returnSourceDocuments: true option. This is not compatible with the SimpleSequentialChain.

To resolve this issue, you need to ensure that all chains used within the SimpleSequentialChain only produce one output. You can do this by modifying the RetrievalQAChain or replacing it with a chain that only produces one output.

Here is the relevant part of your code that is causing the issue:

vectorChain = new RetrievalQAChain({
  combineDocumentsChain: loadQAStuffChain(model),
  retriever: vectoreStore.asRetriever(),
  returnSourceDocuments: true,
});

overallChain = new SimpleSequentialChain({
  chains: [reviewChain1, vectorChain],
  verbose: true,
});

In this code, RetrievalQAChain is being used as vectorChain and is producing more than one output because of the returnSourceDocuments: true option, which is causing the error. You need to modify this part of your code to ensure that all chains used within the SimpleSequentialChain only produce one output.

For example, you could modify your RetrievalQAChain to only return the answer, not the source documents:

vectorChain = new RetrievalQAChain({
  combineDocumentsChain: loadQAStuffChain(model),
  retriever: vectoreStore.asRetriever(),
  returnSourceDocuments: false, // Only return the answer, not the source documents
});

I hope this helps! Let me know if you have any other questions.

Sources

• langchain/src/chains/tests/simple_sequential_chain.test.ts
• langchain/src/chains/sequential_chain.ts
• langchain/src/chains/tests/simple_sequential_chain.int.test.ts

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