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Use with LLMChains

For convenience, you can add an output parser to an LLMChain. This will automatically call .parse() on the output.

Don't forget to put the formatting instructions in the prompt!

import { z } from "zod";
import { ChatOpenAI } from "langchain/chat_models/openai";
import { PromptTemplate } from "langchain/prompts";
import { LLMChain } from "langchain/chains";
import {
  StructuredOutputParser,
  OutputFixingParser,
} from "langchain/output_parsers";

const outputParser = StructuredOutputParser.fromZodSchema(
  z
    .array(
      z.object({
        fields: z.object({
          Name: z.string().describe("The name of the country"),
          Capital: z.string().describe("The country's capital"),
        }),
      })
    )
    .describe("An array of Airtable records, each representing a country")
);

const chatModel = new ChatOpenAI({
  modelName: "gpt-4", // Or gpt-3.5-turbo
  temperature: 0, // For best results with the output fixing parser
});

const outputFixingParser = OutputFixingParser.fromLLM(chatModel, outputParser);

// Don't forget to include formatting instructions in the prompt!
const prompt = new PromptTemplate({
  template: `Answer the user's question as best you can:\n{format_instructions}\n{query}`,
  inputVariables: ["query"],
  partialVariables: {
    format_instructions: outputFixingParser.getFormatInstructions(),
  },
});

const answerFormattingChain = new LLMChain({
  llm: chatModel,
  prompt,
  outputKey: "records", // For readability - otherwise the chain output will default to a property named "text"
  outputParser: outputFixingParser,
});

const result = await answerFormattingChain.call({
  query: "List 5 countries.",
});

console.log(JSON.stringify(result.records, null, 2));

/*
[
  {
    "fields": {
      "Name": "United States",
      "Capital": "Washington, D.C."
    }
  },
  {
    "fields": {
      "Name": "Canada",
      "Capital": "Ottawa"
    }
  },
  {
    "fields": {
      "Name": "Germany",
      "Capital": "Berlin"
    }
  },
  {
    "fields": {
      "Name": "Japan",
      "Capital": "Tokyo"
    }
  },
  {
    "fields": {
      "Name": "Australia",
      "Capital": "Canberra"
    }
  }
]
*/

API Reference: