akka.persistence.journal

Interface WriteEventAdapter

All Known Subinterfaces:

EventAdapter

All Known Implementing Classes:

EventAdapters.CombinedReadEventAdapter, IdentityEventAdapter$, NoopReadEventAdapter, NoopWriteEventAdapter

public interface 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

Method Summary

Modifier and Type	Method and Description
java.lang.String	manifest(java.lang.Object event) Return the manifest (type hint) that will be provided in the fromJournal method.
java.lang.Object	toJournal(java.lang.Object event) Convert domain event to journal event type.

Method Detail

manifest

java.lang.String manifest(java.lang.Object event)

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

Parameters:

event - (undocumented)

Returns:

(undocumented)

toJournal

java.lang.Object toJournal(java.lang.Object event)

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:

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