This class will be removed in 1.0.0. See below for an example implementation using createRetrievalChain.

Class for conducting conversational question-answering tasks with a retrieval component. Extends the BaseChain class and implements the ConversationalRetrievalQAChainInput interface.

import { ChatAnthropic } from "@langchain/anthropic";
import {
ChatPromptTemplate,
MessagesPlaceholder,
} from "@langchain/core/prompts";
import { BaseMessage } from "@langchain/core/messages";
import { createStuffDocumentsChain } from "langchain/chains/combine_documents";
import { createHistoryAwareRetriever } from "langchain/chains/history_aware_retriever";
import { createRetrievalChain } from "langchain/chains/retrieval";

const retriever = ...your retriever;
const llm = new ChatAnthropic();

// Contextualize question
const contextualizeQSystemPrompt = `
Given a chat history and the latest user question
which might reference context in the chat history,
formulate a standalone question which can be understood
without the chat history. Do NOT answer the question, just
reformulate it if needed and otherwise return it as is.`;
const contextualizeQPrompt = ChatPromptTemplate.fromMessages([
["system", contextualizeQSystemPrompt],
new MessagesPlaceholder("chat_history"),
["human", "{input}"],
]);
const historyAwareRetriever = await createHistoryAwareRetriever({
llm,
retriever,
rephrasePrompt: contextualizeQPrompt,
});

// Answer question
const qaSystemPrompt = `
You are an assistant for question-answering tasks. Use
the following pieces of retrieved context to answer the
question. If you don't know the answer, just say that you
don't know. Use three sentences maximum and keep the answer
concise.
\n\n
{context}`;
const qaPrompt = ChatPromptTemplate.fromMessages([
["system", qaSystemPrompt],
new MessagesPlaceholder("chat_history"),
["human", "{input}"],
]);

// Below we use createStuffDocuments_chain to feed all retrieved context
// into the LLM. Note that we can also use StuffDocumentsChain and other
// instances of BaseCombineDocumentsChain.
const questionAnswerChain = await createStuffDocumentsChain({
llm,
prompt: qaPrompt,
});

const ragChain = await createRetrievalChain({
retriever: historyAwareRetriever,
combineDocsChain: questionAnswerChain,
});

// Usage:
const chat_history: BaseMessage[] = [];
const response = await ragChain.invoke({
chat_history,
input: "...",
});

Hierarchy (view full)

Implements

Constructors

Properties

callbacks?: Callbacks
chatHistoryKey: string = "chat_history"
combineDocumentsChain: BaseChain<ChainValues, ChainValues>
inputKey: string = "question"
memory?: BaseMemory
metadata?: Record<string, unknown>
name?: string
questionGeneratorChain: LLMChain<string, LLMType>
retriever: BaseRetrieverInterface<Record<string, any>>
returnGeneratedQuestion: boolean = false
returnSourceDocuments: boolean = false
tags?: string[]
verbose: boolean

Whether to print out response text.

Accessors

Methods

  • Parameters

    • inputs: ChainValues[]
    • Optionalconfig: (RunnableConfig<Record<string, any>> | Callbacks)[]

    Returns Promise<ChainValues[]>

    Use .batch() instead. Will be removed in 0.2.0.

    Call the chain on all inputs in the list

  • Convert a runnable to a tool. Return a new instance of RunnableToolLike which contains the runnable, name, description and schema.

    Type Parameters

    • T extends ChainValues = ChainValues

    Parameters

    • fields: {
          description?: string;
          name?: string;
          schema: ZodType<T, ZodTypeDef, T>;
      }
      • Optionaldescription?: string

        The description of the tool. Falls back to the description on the Zod schema if not provided, or undefined if neither are provided.

      • Optionalname?: string

        The name of the tool. If not provided, it will default to the name of the runnable.

      • schema: ZodType<T, ZodTypeDef, T>

        The Zod schema for the input of the tool. Infers the Zod type from the input type of the runnable.

    Returns RunnableToolLike<ZodType<ToolCall | T, ZodTypeDef, ToolCall | T>, ChainValues>

    An instance of RunnableToolLike which is a runnable that can be used as a tool.

  • Assigns new fields to the dict output of this runnable. Returns a new runnable.

    Parameters

    • mapping: RunnableMapLike<Record<string, unknown>, Record<string, unknown>>

    Returns Runnable<any, any, RunnableConfig<Record<string, any>>>

  • Default implementation of batch, which calls invoke N times. Subclasses should override this method if they can batch more efficiently.

    Parameters

    • inputs: ChainValues[]

      Array of inputs to each batch call.

    • Optionaloptions: Partial<RunnableConfig<Record<string, any>>> | Partial<RunnableConfig<Record<string, any>>>[]

      Either a single call options object to apply to each batch call or an array for each call.

    • OptionalbatchOptions: RunnableBatchOptions & {
          returnExceptions?: false;
      }

    Returns Promise<ChainValues[]>

    An array of RunOutputs, or mixed RunOutputs and errors if batchOptions.returnExceptions is set

  • Parameters

    • inputs: ChainValues[]
    • Optionaloptions: Partial<RunnableConfig<Record<string, any>>> | Partial<RunnableConfig<Record<string, any>>>[]
    • OptionalbatchOptions: RunnableBatchOptions & {
          returnExceptions: true;
      }

    Returns Promise<(ChainValues | Error)[]>

  • Parameters

    • inputs: ChainValues[]
    • Optionaloptions: Partial<RunnableConfig<Record<string, any>>> | Partial<RunnableConfig<Record<string, any>>>[]
    • OptionalbatchOptions: RunnableBatchOptions

    Returns Promise<(ChainValues | Error)[]>

  • Bind arguments to a Runnable, returning a new Runnable.

    Parameters

    • kwargs: Partial<RunnableConfig<Record<string, any>>>

    Returns Runnable<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>

    A new RunnableBinding that, when invoked, will apply the bound args.

  • Parameters

    • values: ChainValues & {
          signal?: AbortSignal;
          timeout?: number;
      }
    • Optionalconfig: RunnableConfig<Record<string, any>> | Callbacks
    • Optionaltags: string[]

    Returns Promise<ChainValues>

    Use .invoke() instead. Will be removed in 0.2.0.

    Run the core logic of this chain and add to output if desired.

    Wraps _call and handles memory.

  • Parameters

    • Optional_: RunnableConfig<Record<string, any>>

    Returns Graph

  • Parameters

    • Optionalsuffix: string

    Returns string

  • Invoke the chain with the provided input and returns the output.

    Parameters

    • input: ChainValues

      Input values for the chain run.

    • Optionaloptions: RunnableConfig<Record<string, any>>

    Returns Promise<ChainValues>

    Promise that resolves with the output of the chain run.

  • Return a new Runnable that maps a list of inputs to a list of outputs, by calling invoke() with each input.

    Returns Runnable<ChainValues[], ChainValues[], RunnableConfig<Record<string, any>>>

  • Pick keys from the dict output of this runnable. Returns a new runnable.

    Parameters

    • keys: string | string[]

    Returns Runnable<any, any, RunnableConfig<Record<string, any>>>

  • Create a new runnable sequence that runs each individual runnable in series, piping the output of one runnable into another runnable or runnable-like.

    Type Parameters

    • NewRunOutput

    Parameters

    • coerceable: RunnableLike<ChainValues, NewRunOutput, RunnableConfig<Record<string, any>>>

      A runnable, function, or object whose values are functions or runnables.

    Returns Runnable<ChainValues, Exclude<NewRunOutput, Error>, RunnableConfig<Record<string, any>>>

    A new runnable sequence.

  • Parameters

    • inputs: Record<string, unknown>
    • outputs: Record<string, unknown>
    • returnOnlyOutputs: boolean = false

    Returns Promise<Record<string, unknown>>

  • Parameters

    • input: any
    • Optionalconfig: RunnableConfig<Record<string, any>> | Callbacks

    Returns Promise<string>

    Use .invoke() instead. Will be removed in 0.2.0.

  • Stream output in chunks.

    Parameters

    • input: ChainValues
    • Optionaloptions: Partial<RunnableConfig<Record<string, any>>>

    Returns Promise<IterableReadableStream<ChainValues>>

    A readable stream that is also an iterable.

  • Generate a stream of events emitted by the internal steps of the runnable.

    Use to create an iterator over StreamEvents that provide real-time information about the progress of the runnable, including StreamEvents from intermediate results.

    A StreamEvent is a dictionary with the following schema:

    • event: string - Event names are of the format: on_[runnable_type]_(start|stream|end).
    • name: string - The name of the runnable that generated the event.
    • run_id: string - Randomly generated ID associated with the given execution of the runnable that emitted the event. A child runnable that gets invoked as part of the execution of a parent runnable is assigned its own unique ID.
    • tags: string[] - The tags of the runnable that generated the event.
    • metadata: Record<string, any> - The metadata of the runnable that generated the event.
    • data: Record<string, any>

    Below is a table that illustrates some events that might be emitted by various chains. Metadata fields have been omitted from the table for brevity. Chain definitions have been included after the table.

    ATTENTION This reference table is for the V2 version of the schema.

    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | event                | name             | chunk                           | input                                         | output                                          |
    +======================+==================+=================================+===============================================+=================================================+
    | on_chat_model_start  | [model name]     |                                 | {"messages": [[SystemMessage, HumanMessage]]} |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_chat_model_stream | [model name]     | AIMessageChunk(content="hello") |                                               |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_chat_model_end    | [model name]     |                                 | {"messages": [[SystemMessage, HumanMessage]]} | AIMessageChunk(content="hello world")           |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_llm_start         | [model name]     |                                 | {'input': 'hello'}                            |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_llm_stream        | [model name]     | 'Hello'                         |                                               |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_llm_end           | [model name]     |                                 | 'Hello human!'                                |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_chain_start       | some_runnable    |                                 |                                               |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_chain_stream      | some_runnable    | "hello world!, goodbye world!"  |                                               |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_chain_end         | some_runnable    |                                 | [Document(...)]                               | "hello world!, goodbye world!"                  |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_tool_start        | some_tool        |                                 | {"x": 1, "y": "2"}                            |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_tool_end          | some_tool        |                                 |                                               | {"x": 1, "y": "2"}                              |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_retriever_start   | [retriever name] |                                 | {"query": "hello"}                            |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_retriever_end     | [retriever name] |                                 | {"query": "hello"}                            | [Document(...), ..]                             |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_prompt_start      | [template_name]  |                                 | {"question": "hello"}                         |                                                 |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    | on_prompt_end        | [template_name]  |                                 | {"question": "hello"}                         | ChatPromptValue(messages: [SystemMessage, ...]) |
    +----------------------+------------------+---------------------------------+-----------------------------------------------+-------------------------------------------------+
    

    The "on_chain_*" events are the default for Runnables that don't fit one of the above categories.

    In addition to the standard events above, users can also dispatch custom events.

    Custom events will be only be surfaced with in the v2 version of the API!

    A custom event has following format:

    +-----------+------+-----------------------------------------------------------------------------------------------------------+
    | Attribute | Type | Description                                                                                               |
    +===========+======+===========================================================================================================+
    | name      | str  | A user defined name for the event.                                                                        |
    +-----------+------+-----------------------------------------------------------------------------------------------------------+
    | data      | Any  | The data associated with the event. This can be anything, though we suggest making it JSON serializable.  |
    +-----------+------+-----------------------------------------------------------------------------------------------------------+
    

    Here's an example:

    import { RunnableLambda } from "@langchain/core/runnables";
    import { dispatchCustomEvent } from "@langchain/core/callbacks/dispatch";
    // Use this import for web environments that don't support "async_hooks"
    // and manually pass config to child runs.
    // import { dispatchCustomEvent } from "@langchain/core/callbacks/dispatch/web";

    const slowThing = RunnableLambda.from(async (someInput: string) => {
    // Placeholder for some slow operation
    await new Promise((resolve) => setTimeout(resolve, 100));
    await dispatchCustomEvent("progress_event", {
    message: "Finished step 1 of 2",
    });
    await new Promise((resolve) => setTimeout(resolve, 100));
    return "Done";
    });

    const eventStream = await slowThing.streamEvents("hello world", {
    version: "v2",
    });

    for await (const event of eventStream) {
    if (event.event === "on_custom_event") {
    console.log(event);
    }
    }

    Parameters

    • input: ChainValues
    • options: Partial<RunnableConfig<Record<string, any>>> & {
          version: "v1" | "v2";
      }
    • OptionalstreamOptions: Omit<EventStreamCallbackHandlerInput, "autoClose">

    Returns IterableReadableStream<StreamEvent>

  • Parameters

    • input: ChainValues
    • options: Partial<RunnableConfig<Record<string, any>>> & {
          encoding: "text/event-stream";
          version: "v1" | "v2";
      }
    • OptionalstreamOptions: Omit<EventStreamCallbackHandlerInput, "autoClose">

    Returns IterableReadableStream<Uint8Array>

  • Stream all output from a runnable, as reported to the callback system. This includes all inner runs of LLMs, Retrievers, Tools, etc. Output is streamed as Log objects, which include a list of jsonpatch ops that describe how the state of the run has changed in each step, and the final state of the run. The jsonpatch ops can be applied in order to construct state.

    Parameters

    • input: ChainValues
    • Optionaloptions: Partial<RunnableConfig<Record<string, any>>>
    • OptionalstreamOptions: Omit<LogStreamCallbackHandlerInput, "autoClose">

    Returns AsyncGenerator<RunLogPatch, any, unknown>

  • Default implementation of transform, which buffers input and then calls stream. Subclasses should override this method if they can start producing output while input is still being generated.

    Parameters

    • generator: AsyncGenerator<ChainValues, any, unknown>
    • options: Partial<RunnableConfig<Record<string, any>>>

    Returns AsyncGenerator<ChainValues, any, unknown>

  • Bind config to a Runnable, returning a new Runnable.

    Parameters

    • config: RunnableConfig<Record<string, any>>

      New configuration parameters to attach to the new runnable.

    Returns RunnableBinding<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>

    A new RunnableBinding with a config matching what's passed.

  • Create a new runnable from the current one that will try invoking other passed fallback runnables if the initial invocation fails.

    Parameters

    • fields: {
          fallbacks: Runnable<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>[];
      } | Runnable<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>[]

    Returns RunnableWithFallbacks<ChainValues, ChainValues>

    A new RunnableWithFallbacks.

  • Bind lifecycle listeners to a Runnable, returning a new Runnable. The Run object contains information about the run, including its id, type, input, output, error, startTime, endTime, and any tags or metadata added to the run.

    Parameters

    • params: {
          onEnd?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>);
          onError?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>);
          onStart?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>);
      }

      The object containing the callback functions.

      • OptionalonEnd?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>)

        Called after the runnable finishes running, with the Run object.

          • (run, config?): void | Promise<void>
          • Parameters

            • run: Run
            • Optionalconfig: RunnableConfig<Record<string, any>>

            Returns void | Promise<void>

      • OptionalonError?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>)

        Called if the runnable throws an error, with the Run object.

          • (run, config?): void | Promise<void>
          • Parameters

            • run: Run
            • Optionalconfig: RunnableConfig<Record<string, any>>

            Returns void | Promise<void>

      • OptionalonStart?: ((run: Run, config?: RunnableConfig<Record<string, any>>) => void | Promise<void>)

        Called before the runnable starts running, with the Run object.

          • (run, config?): void | Promise<void>
          • Parameters

            • run: Run
            • Optionalconfig: RunnableConfig<Record<string, any>>

            Returns void | Promise<void>

    Returns Runnable<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>

  • Add retry logic to an existing runnable.

    Parameters

    • Optionalfields: {
          onFailedAttempt?: RunnableRetryFailedAttemptHandler;
          stopAfterAttempt?: number;
      }
      • OptionalonFailedAttempt?: RunnableRetryFailedAttemptHandler
      • OptionalstopAfterAttempt?: number

    Returns RunnableRetry<ChainValues, ChainValues, RunnableConfig<Record<string, any>>>

    A new RunnableRetry that, when invoked, will retry according to the parameters.

  • Static method to create a new ConversationalRetrievalQAChain from a BaseLanguageModel and a BaseRetriever.

    Parameters

    • llm: BaseLanguageModelInterface<any, BaseLanguageModelCallOptions>

      BaseLanguageModelInterface instance used to generate a new question.

    • retriever: BaseRetrieverInterface<Record<string, any>>

      BaseRetrieverInterface instance used to retrieve relevant documents.

    • options: {
          outputKey?: string;
          qaChainOptions?: QAChainParams;
          qaTemplate?: string;
          questionGeneratorChainOptions?: {
              llm?: BaseLanguageModelInterface<any, BaseLanguageModelCallOptions>;
              template?: string;
          };
          questionGeneratorTemplate?: string;
          returnSourceDocuments?: boolean;
      } & Omit<ConversationalRetrievalQAChainInput, "combineDocumentsChain" | "retriever" | "questionGeneratorChain"> = {}

    Returns ConversationalRetrievalQAChain

    A new instance of ConversationalRetrievalQAChain.

  • Static method to convert the chat history input into a formatted string.

    Parameters

    • chatHistory: string | BaseMessage[] | string[][]

      Chat history input which can be a string, an array of BaseMessage instances, or an array of string arrays.

    Returns string

    A formatted string representing the chat history.

  • Parameters

    • thing: any

    Returns thing is Runnable<any, any, RunnableConfig<Record<string, any>>>