Package org.axonframework.queryhandling

Interface QueryBus

All Superinterfaces:
MessageDispatchInterceptorSupport<QueryMessage<?,?>>, MessageHandlerInterceptorSupport<QueryMessage<?,?>>
All Known Implementing Classes:
AxonServerQueryBus, SimpleQueryBus
public interface QueryBus extends MessageHandlerInterceptorSupport<QueryMessage<?,?>>, MessageDispatchInterceptorSupport<QueryMessage<?,?>>
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/responseType.
Since:
3.1
Author:
Marc Gathier, Allard Buijze

  • Method Details

    • subscribe

      <R> Registration subscribe(@Nonnull String queryName, @Nonnull Type responseType, @Nonnull MessageHandler<? super QueryMessage<?,R>> handler)
      Subscribe the given handler to queries with the given queryName and responseType. Multiple handlers may subscribe to the same combination of queryName/responseType.
      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(@Nonnull 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

    • streamingQuery

      default <Q, R> org.reactivestreams.Publisher<QueryResponseMessage<R>> streamingQuery(StreamingQueryMessage<Q,R> query)
      Builds a Publisher of responses to the given query. The actual query is not dispatched until there is a subscription to the result. The query is dispatched to a single query handler. Implementations may opt for invoking several query handlers and then choosing a response from single one for performance or resilience reasons.

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

      Type Parameters:
      Q - the payload type of the streaming query
      R - the response type of the streaming query
      Parameters:
      query - the streaming query message
      Returns:
      a Publisher of responses

    • scatterGather

      <Q, R> Stream<QueryResponseMessage<R>> scatterGather(@Nonnull QueryMessage<Q,R> query, long timeout, @Nonnull TimeUnit unit)
      Dispatch the given query to all QueryHandlers subscribed to the given query's queryName/responseType. 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

    • subscriptionQuery

      default <Q, I, U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>> subscriptionQuery(@Nonnull SubscriptionQueryMessage<Q,I,U> query)
      Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType. The result is lazily created and there will be no execution of the query handler before there is a subscription to the initial result. In order not to miss updates, the query bus will queue all updates which happen after the subscription query is done and once the subscription to the flux is made, these updates will be emitted.

      If there is an error during retrieving or consuming initial result, stream for incremental updates is NOT interrupted.

      If there is an error during emitting an update, subscription is cancelled causing further emits not reaching the destination.

      The buffer size which accumulates the updates (not to be missed) is Queues.SMALL_BUFFER_SIZE.

      Type Parameters:
      Q - the payload type of the query
      I - the response type of the query
      U - the incremental response types of the query
      Parameters:
      query - the query
      Returns:
      query result containing initial result and incremental updates

    • subscriptionQuery

      @Deprecated default <Q, I, U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>> subscriptionQuery(@Nonnull SubscriptionQueryMessage<Q,I,U> query, SubscriptionQueryBackpressure backpressure, int updateBufferSize)
      Deprecated.
      in favour of using {subscriptionQuery(SubscriptionQueryMessage, int)}
      Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType. The result is lazily created and there will be no execution of the query handler before there is a subscription to the initial result. In order not to miss updates, the query bus will queue all updates which happen after the subscription query is done and once the subscription to the flux is made, these updates will be emitted.

      If there is an error during retrieving or consuming initial result, stream for incremental updates is NOT interrupted.

      If there is an error during emitting an update, subscription is cancelled causing further emits not reaching the destination.

      Provided backpressure mechanism will be used to deal with fast emitters.

      Type Parameters:
      Q - the payload type of the query
      I - the response type of the query
      U - the incremental response types of the query
      Parameters:
      query - the query
      backpressure - the backpressure mechanism to be used for emitting updates
      updateBufferSize - the size of buffer which accumulates updates before subscription to the flux is made
      Returns:
      query result containing initial result and incremental updates

    • subscriptionQuery

      default <Q, I, U> SubscriptionQueryResult<QueryResponseMessage<I>,SubscriptionQueryUpdateMessage<U>> subscriptionQuery(@Nonnull SubscriptionQueryMessage<Q,I,U> query, int updateBufferSize)
      Dispatch the given query to a single QueryHandler subscribed to the given query's queryName/initialResponseType/updateResponseType. The result is lazily created and there will be no execution of the query handler before there is a subscription to the initial result. In order not to miss updates, the query bus will queue all updates which happen after the subscription query is done and once the subscription to the flux is made, these updates will be emitted.

      If there is an error during retrieving or consuming initial result, stream for incremental updates is NOT interrupted.

      If there is an error during emitting an update, subscription is cancelled causing further emits not reaching the destination.

      Type Parameters:
      Q - the payload type of the query
      I - the response type of the query
      U - the incremental response types of the query
      Parameters:
      query - the query
      updateBufferSize - the size of buffer which accumulates updates before subscription to the flux is made
      Returns:
      query result containing initial result and incremental updates

    • queryUpdateEmitter

      QueryUpdateEmitter queryUpdateEmitter()
      Gets the QueryUpdateEmitter associated with this QueryBus.
      Returns:
      the associated QueryUpdateEmitter