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conversational_retrieval_chain.ts
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conversational_retrieval_chain.ts
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import type { BaseLanguageModelInterface } from "@langchain/core/language_models/base";
import type { BaseRetrieverInterface } from "@langchain/core/retrievers";
import { PromptTemplate } from "@langchain/core/prompts";
import { BaseMessage, HumanMessage, AIMessage } from "@langchain/core/messages";
import { ChainValues } from "@langchain/core/utils/types";
import { CallbackManagerForChainRun } from "@langchain/core/callbacks/manager";
import { SerializedChatVectorDBQAChain } from "./serde.js";
import { BaseChain, ChainInputs } from "./base.js";
import { LLMChain } from "./llm_chain.js";
import { QAChainParams, loadQAChain } from "./question_answering/load.js";
// eslint-disable-next-line @typescript-eslint/no-explicit-any
export type LoadValues = Record<string, any>;
const question_generator_template = `Given the following conversation and a follow up question, rephrase the follow up question to be a standalone question.
Chat History:
{chat_history}
Follow Up Input: {question}
Standalone question:`;
/**
* Interface for the input parameters of the
* ConversationalRetrievalQAChain class.
*/
export interface ConversationalRetrievalQAChainInput extends ChainInputs {
retriever: BaseRetrieverInterface;
combineDocumentsChain: BaseChain;
questionGeneratorChain: LLMChain;
returnSourceDocuments?: boolean;
returnGeneratedQuestion?: boolean;
inputKey?: string;
}
/**
* Class for conducting conversational question-answering tasks with a
* retrieval component. Extends the BaseChain class and implements the
* ConversationalRetrievalQAChainInput interface.
* @example
* ```typescript
* const model = new ChatAnthropic({});
*
* const text = fs.readFileSync("state_of_the_union.txt", "utf8");
*
* const textSplitter = new RecursiveCharacterTextSplitter({ chunkSize: 1000 });
* const docs = await textSplitter.createDocuments([text]);
*
* const vectorStore = await HNSWLib.fromDocuments(docs, new OpenAIEmbeddings());
*
* const chain = ConversationalRetrievalQAChain.fromLLM(
* model,
* vectorStore.asRetriever(),
* );
*
* const question = "What did the president say about Justice Breyer?";
*
* const res = await chain.call({ question, chat_history: "" });
* console.log(res);
*
* const chatHistory = `${question}\n${res.text}`;
* const followUpRes = await chain.call({
* question: "Was that nice?",
* chat_history: chatHistory,
* });
* console.log(followUpRes);
*
* ```
*/
export class ConversationalRetrievalQAChain
extends BaseChain
implements ConversationalRetrievalQAChainInput
{
static lc_name() {
return "ConversationalRetrievalQAChain";
}
inputKey = "question";
chatHistoryKey = "chat_history";
get inputKeys() {
return [this.inputKey, this.chatHistoryKey];
}
get outputKeys() {
return this.combineDocumentsChain.outputKeys.concat(
this.returnSourceDocuments ? ["sourceDocuments"] : []
);
}
retriever: BaseRetrieverInterface;
combineDocumentsChain: BaseChain;
questionGeneratorChain: LLMChain;
returnSourceDocuments = false;
returnGeneratedQuestion = false;
constructor(fields: ConversationalRetrievalQAChainInput) {
super(fields);
this.retriever = fields.retriever;
this.combineDocumentsChain = fields.combineDocumentsChain;
this.questionGeneratorChain = fields.questionGeneratorChain;
this.inputKey = fields.inputKey ?? this.inputKey;
this.returnSourceDocuments =
fields.returnSourceDocuments ?? this.returnSourceDocuments;
this.returnGeneratedQuestion =
fields.returnGeneratedQuestion ?? this.returnGeneratedQuestion;
}
/**
* Static method to convert the chat history input into a formatted
* string.
* @param chatHistory Chat history input which can be a string, an array of BaseMessage instances, or an array of string arrays.
* @returns A formatted string representing the chat history.
*/
static getChatHistoryString(
chatHistory: string | BaseMessage[] | string[][]
) {
let historyMessages: BaseMessage[];
if (Array.isArray(chatHistory)) {
// TODO: Deprecate on a breaking release
if (
Array.isArray(chatHistory[0]) &&
typeof chatHistory[0][0] === "string"
) {
console.warn(
"Passing chat history as an array of strings is deprecated.\nPlease see https://js.langchain.com/docs/modules/chains/popular/chat_vector_db#externally-managed-memory for more information."
);
historyMessages = chatHistory.flat().map((stringMessage, i) => {
if (i % 2 === 0) {
return new HumanMessage(stringMessage);
} else {
return new AIMessage(stringMessage);
}
});
} else {
historyMessages = chatHistory as BaseMessage[];
}
return historyMessages
.map((chatMessage) => {
if (chatMessage._getType() === "human") {
return `Human: ${chatMessage.content}`;
} else if (chatMessage._getType() === "ai") {
return `Assistant: ${chatMessage.content}`;
} else {
return `${chatMessage.content}`;
}
})
.join("\n");
}
return chatHistory;
}
/** @ignore */
async _call(
values: ChainValues,
runManager?: CallbackManagerForChainRun
): Promise<ChainValues> {
if (!(this.inputKey in values)) {
throw new Error(`Question key ${this.inputKey} not found.`);
}
if (!(this.chatHistoryKey in values)) {
throw new Error(`Chat history key ${this.chatHistoryKey} not found.`);
}
const question: string = values[this.inputKey];
const chatHistory: string =
ConversationalRetrievalQAChain.getChatHistoryString(
values[this.chatHistoryKey]
);
let newQuestion = question;
if (chatHistory.length > 0) {
const result = await this.questionGeneratorChain.call(
{
question,
chat_history: chatHistory,
},
runManager?.getChild("question_generator")
);
const keys = Object.keys(result);
if (keys.length === 1) {
newQuestion = result[keys[0]];
} else {
throw new Error(
"Return from llm chain has multiple values, only single values supported."
);
}
}
const docs = await this.retriever.getRelevantDocuments(
newQuestion,
runManager?.getChild("retriever")
);
const inputs = {
question: newQuestion,
input_documents: docs,
chat_history: chatHistory,
};
let result = await this.combineDocumentsChain.call(
inputs,
runManager?.getChild("combine_documents")
);
if (this.returnSourceDocuments) {
result = {
...result,
sourceDocuments: docs,
};
}
if (this.returnGeneratedQuestion) {
result = {
...result,
generatedQuestion: newQuestion,
};
}
return result;
}
_chainType(): string {
return "conversational_retrieval_chain";
}
static async deserialize(
_data: SerializedChatVectorDBQAChain,
_values: LoadValues
): Promise<ConversationalRetrievalQAChain> {
throw new Error("Not implemented.");
}
serialize(): SerializedChatVectorDBQAChain {
throw new Error("Not implemented.");
}
/**
* Static method to create a new ConversationalRetrievalQAChain from a
* BaseLanguageModel and a BaseRetriever.
* @param llm {@link BaseLanguageModelInterface} instance used to generate a new question.
* @param retriever {@link BaseRetrieverInterface} instance used to retrieve relevant documents.
* @param options.returnSourceDocuments Whether to return source documents in the final output
* @param options.questionGeneratorChainOptions Options to initialize the standalone question generation chain used as the first internal step
* @param options.qaChainOptions {@link QAChainParams} used to initialize the QA chain used as the second internal step
* @returns A new instance of ConversationalRetrievalQAChain.
*/
static fromLLM(
llm: BaseLanguageModelInterface,
retriever: BaseRetrieverInterface,
options: {
outputKey?: string; // not used
returnSourceDocuments?: boolean;
/** @deprecated Pass in questionGeneratorChainOptions.template instead */
questionGeneratorTemplate?: string;
/** @deprecated Pass in qaChainOptions.prompt instead */
qaTemplate?: string;
questionGeneratorChainOptions?: {
llm?: BaseLanguageModelInterface;
template?: string;
};
qaChainOptions?: QAChainParams;
} & Omit<
ConversationalRetrievalQAChainInput,
"retriever" | "combineDocumentsChain" | "questionGeneratorChain"
> = {}
): ConversationalRetrievalQAChain {
const {
questionGeneratorTemplate,
qaTemplate,
qaChainOptions = {
type: "stuff",
prompt: qaTemplate
? PromptTemplate.fromTemplate(qaTemplate)
: undefined,
},
questionGeneratorChainOptions,
verbose,
...rest
} = options;
const qaChain = loadQAChain(llm, qaChainOptions);
const questionGeneratorChainPrompt = PromptTemplate.fromTemplate(
questionGeneratorChainOptions?.template ??
questionGeneratorTemplate ??
question_generator_template
);
const questionGeneratorChain = new LLMChain({
prompt: questionGeneratorChainPrompt,
llm: questionGeneratorChainOptions?.llm ?? llm,
verbose,
});
const instance = new this({
retriever,
combineDocumentsChain: qaChain,
questionGeneratorChain,
verbose,
...rest,
});
return instance;
}
}