RetrievalQAChain class

Chain for question-answering against the documents retrieved by the retriever.

It retrieves the documents using the retriever and then combines them using the combineDocumentsChain.

For convenience, you can instantiate this chain using the factory constructor RetrievalQAChain.fromLlm. By default, it uses a prompt template optimized for question answering that includes the retrieved documents and the question to answer. The documents are inserted in the prompt using a StuffDocumentsQAChain.

The chain returns two outputs:

  • result (or the output key specified in the constructor): the answer to the question.
  • source_documents: the documents used to answer the question.

Note: as the chain returns two outputs you can only call it using the call method. The run method is not supported.

Example:

final retriever = VectorStoreRetriever(vectorStore: vectorStore);
final retrievalQA = RetrievalQAChain.fromLlm(
  llm: llm,
  retriever: retriever,
);
final res = await retrievalQA({
  RetrievalQAChain.defaultInputKey: 'What did I say?',
});
final answer = res[RetrievalQAChain.defaultOutputKey];
final docs = res[RetrievalQAChain.sourceDocumentsOutputKey];

If you need more flexibility, you can use the primary constructor which allows you to specify the retriever and the combineDocumentsChain. Your prompt should include the {context} and {question} variables to be replaced by the documents and the question respectively.

Example:

final llmChain = LLMChain(prompt: prompt, llm: llm);
final stuffChain = StuffDocumentsChain(llmChain: llmChain);
final retrievalQA = RetrievalQAChain(
  retriever: retriever,
  combineDocumentsChain: stuffChain,
);
final res = await retrievalQA({
  RetrievalQAChain.defaultInputKey: 'What did I say?',
});
Inheritance
Available Extensions

Constructors

RetrievalQAChain({required Retriever<RetrieverOptions> retriever, required BaseCombineDocumentsChain combineDocumentsChain, String inputKey = defaultInputKey, String outputKey = defaultOutputKey, String combineDocumentsChainInputKey = BaseCombineDocumentsChain.defaultInputKey})
Chain for question-answering against the documents retrieved by the retriever.
const
RetrievalQAChain.fromLlm({required BaseLanguageModel<Object, LanguageModelOptions, LanguageModelResult<Object>> llm, required Retriever<RetrieverOptions> retriever, PromptTemplate? prompt})
Creates a RetrievalQAChain from a BaseLanguageModel and a Retriever.
factory

Properties

chainType → String
Return the string type key uniquely identifying this class of chain.
no setteroverride
combineDocumentsChain → BaseCombineDocumentsChain
Chain to use to combine the documents.
final
combineDocumentsChainInputKey → String
Key to use for inputting the documents to combineDocumentsChain.
final
defaultOptions → ChainOptions
The default options to use when invoking the Runnable.
finalinherited
hashCode → int
The hash code for this object.
no setterinherited
inputKey → String
Key to use for the input query.
final
inputKeys → Set<String>
Input keys for this chain.
no setteroverride
memory → BaseMemory?
Memory to use for this chain.
finalinherited
outputKey → String
Key to use for output text.
final
outputKeys → Set<String>
Output keys for this chain.
no setteroverride
retriever → Retriever<RetrieverOptions>
Retriever to use.
final
runOutputKey → String
Output key from where the run method needs to take the return value.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

apply(List<ChainValues> inputs) → Future<List<ChainValues>>
Call the chain on all inputs in the list.
inherited
batch(List<ChainValues> inputs, {List<ChainOptions>? options}) → Future<List<ChainValues>>
Batches the invocation of the Runnable on the given inputs.
inherited
bind(ChainOptions options) → RunnableBinding<ChainValues, ChainOptions, ChainValues>
Binds the Runnable to the given options.
inherited
call(dynamic input, {bool returnOnlyOutputs = false}) → Future<ChainValues>
Runs the core logic of this chain with the given values. If memory is not null, it will be used to load and save values.
inherited
callInternal(ChainValues inputs) → Future<ChainValues>
Call method to be implemented by subclasses (called by call). This is where the core logic of the chain should be implemented.
override
close() → void
Cleans up any resources associated with it the Runnable.
inherited
getCompatibleOptions(RunnableOptions? options) → ChainOptions?
Returns the given options if they are compatible with the Runnable, otherwise returns null.
inherited
invoke(ChainValues input, {ChainOptions? options}) → Future<ChainValues>
Runs the core logic of this chain with the given input.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
pipe<NewRunOutput extends Object?, NewCallOptions extends RunnableOptions>(Runnable<ChainValues, NewCallOptions, NewRunOutput> next) → RunnableSequence<ChainValues, NewRunOutput>
Pipes the output of this Runnable into another Runnable using a RunnableSequence.
inherited
run(dynamic input) → Future<String>
Convenience method for executing chain when there's a single string output.
inherited
stream(ChainValues input, {ChainOptions? options}) → Stream<ChainValues>
Streams the output of invoking the Runnable on the given input.
inherited
streamFromInputStream(Stream<ChainValues> inputStream, {ChainOptions? options}) → Stream<ChainValues>
Streams the output of invoking the Runnable on the given inputStream.
inherited
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited

Constants

defaultInputKey → const String
Default input key for the query.
defaultOutputKey → const String
Default output key for the output of the chain.
questionPromptVar → const String
Prompt variable to use for the question.
sourceDocumentsOutputKey → const String
Output key to use for returning the source documents.