Package org.apache.pekko.persistence.typed

Class EventAdapter<E,P>

java.lang.Object
org.apache.pekko.persistence.typed.EventAdapter<E,P>
public abstract class EventAdapter<E,P> extends Object
Facility to convert from and to specialised data models, as may be required by specialized persistence Journals. Typical use cases include (but are not limited to):
  • extracting events from "envelopes"
  • adapting events from a "domain model" to the "data model", e.g. converting to the Journals storage format, such as JSON, BSON or any specialised binary format
  • adapting events from a "data model" to the "domain model"
  • adding metadata that is understood by the journal
  • migration by splitting up events into sequences of other events
  • migration filtering out unused events, or replacing an event with another

  • Constructor Details

    • EventAdapter

      public EventAdapter()

  • Method Details

    • fromJournal

      public abstract EventSeq<E> fromJournal(P p, String manifest)
      Transform the event on recovery from the journal. Note that this is not called in any read side so will need to be applied manually when using Query.

      Convert a event from its journal model to the applications domain model.

      One event may be adapter into multiple (or none) events which should be delivered to the EventSourcedBehavior. Use the specialised EventSeq.single method to emit exactly one event, or EventSeq.empty in case the adapter is not handling this event.

      Parameters:
      p - event to be adapted before delivering to the EventSourcedBehavior
      manifest - optionally provided manifest (type hint) in case the Adapter has stored one for this event, "" if none
      Returns:
      sequence containing the adapted events (possibly zero) which will be delivered to the EventSourcedBehavior

    • manifest

      public abstract String manifest(E event)
      Return the manifest (type hint) that will be provided in the fromJournal method. Use "" if manifest is not needed.

    • toJournal

      public abstract P toJournal(E e)
      Convert domain event to journal event type.

      Some journal may require a specific type to be returned to them, for example if a primary key has to be associated with each event then a journal may require adapters to return com.example.myjournal.EventWithPrimaryKey(event, key).

      The toJournal adaptation must be an 1-to-1 transformation. It is not allowed to drop incoming events during the toJournal adaptation.

      Parameters:
      e - the application-side domain event to be adapted to the journal model
      Returns:
      the adapted event object, possibly the same object if no adaptation was performed