org.axonframework.queryhandling

Interface QueryBus

All Known Implementing Classes:

SimpleQueryBus

public interface QueryBus

The mechanism that dispatches Query objects to their appropriate QueryHandlers. QueryHandlers can subscribe and un-subscribe to specific queries (identified by their QueryMessage.getQueryName() and QueryMessage.getResponseType() on the query bus. There may be multiple handlers for each combination of queryName/responseName.

Since:

3.1

Author:

Marc Gathier, Allard Buijze

Method Summary

Modifier and Type	Method and Description
<Q,R> CompletableFuture<QueryResponseMessage<R>>	query(QueryMessage<Q,R> query) Dispatch the given query to a single QueryHandler subscribed to the given query's queryName and responseType.
<Q,R> Stream<QueryResponseMessage<R>>	scatterGather(QueryMessage<Q,R> query, long timeout, TimeUnit unit) Dispatch the given query to all QueryHandlers subscribed to the given query's queryName/responseName.
<R> Registration	subscribe(String queryName, Type responseType, MessageHandler<? super QueryMessage<?,R>> handler) Subscribe the given handler to queries with the given queryName and responseName.

Method Detail

subscribe

<R> Registration subscribe(String queryName,
                           Type responseType,
                           MessageHandler<? super QueryMessage<?,R>> handler)

Subscribe the given handler to queries with the given queryName and responseName. Multiple handlers may subscribe to the same combination of queryName/responseName.

Parameters:

queryName - the name of the query request to subscribe

responseType - the type of response the subscribed component answers with

handler - a handler that implements the query

Returns:

a handle to un-subscribe the query handler

query

<Q,R> CompletableFuture<QueryResponseMessage<R>> query(QueryMessage<Q,R> query)

Dispatch the given query to a single QueryHandler subscribed to the given query's queryName and responseType. This method returns all values returned by the Query Handler as a Collection. This may or may not be the exact collection as defined in the Query Handler.

If the Query Handler defines a single return object (i.e. not a collection or array), that object is returned as the sole entry in a singleton collection.

When no handlers are available that can answer the given query, the returned CompletableFuture will be completed with a NoHandlerForQueryException.

Type Parameters:

Q - the payload type of the query

R - the response type of the query

Parameters:

query - the query

Returns:

a CompletableFuture that resolves when the response is available

scatterGather

<Q,R> Stream<QueryResponseMessage<R>> scatterGather(QueryMessage<Q,R> query,
                                                    long timeout,
                                                    TimeUnit unit)

Dispatch the given query to all QueryHandlers subscribed to the given query's queryName/responseName. Returns a stream of results which blocks until all handlers have processed the request or when the timeout occurs.

If no handlers are available to provide a result, or when all available handlers throw an exception while attempting to do so, the returned Stream is empty.

Note that any terminal operation (such as Stream.forEach(Consumer)) on the Stream may cause it to block until the timeout has expired, awaiting additional data to include in the stream.

Type Parameters:

Q - the payload type of the query

R - the response type of the query

Parameters:

query - the query

timeout - time to wait for results

unit - unit for the timeout

Returns:

stream of query results