Akka/akka.persistence.journal/WriteEventAdapter

WriteEventAdapter

trait WriteEventAdapter

Facility to convert to specialised data models, as may be required by specialized persistence Journals.

Typical use cases include (but are not limited to):

  • adding metadata, a.k.a. "tagging" - by wrapping objects into tagged counterparts

  • manually converting to the Journals storage format, such as JSON, BSON or any specialised binary format

  • splitting up large events into sequences of smaller ones

Source:
EventAdapter.scala
class Object
trait Matchable
class Any

Value members

Abstract methods

def manifest(event: Any): String

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

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

Source:
EventAdapter.scala
def toJournal(event: Any): Any

Convert domain event to journal event type.

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.

Value parameters:
event

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

Source:
EventAdapter.scala