event-schema-unregistered

• Routes: write-events, restore-backup, and import-events
• Description: /events/<index>: event type has no registered schema, and schemas are required when writing events, with the place of the event in its list, counting from 0, and event type has no registered schema, and schemas are required when restoring a backup or importing events
• Details: When writing events, event, the place of the event in its list, counting from 0, and value, its event type. When restoring a backup or importing events, eventId, the ID of the event, and value, its event type.

Why It Happens#

The server was started with --require-event-schemas, which enforces known event types: an event can only be written if its type has a schema. An event of a type that nobody has registered a schema for yet, such as a new one, is refused, and with it the whole write. Without the flag, which is off by default, events of any type are written.

Restoring a backup follows the same rule: every event of the backup needs a schema for its type that the backup registers before it. So does importing events: every event needs a schema for its type that was registered before the import.

How to Fix It#

Register a schema for the event type, and then send the write again, which then succeeds as far as its events match the schema. A restore needs an empty database, so no schema can be registered before it, see store-not-empty: restore such a backup on a server started without --require-event-schemas. An import takes a database that holds schemas, so register the missing schema, and import the events again.

Example#

For a write of an event of the type io.eventsourcingdb.library.book-borrowed, which has no schema, while the database requires schemas, EventSourcingDB answers with this error, as a line of the stream, and then ends the stream with its end item:

{
  "type": "error",
  "data": {
    "code": "https://docs.eventsourcingdb.io/errors/event-schema-unregistered",
    "description": "/events/0: event type has no registered schema, and schemas are required",
    "details": {
      "event": 0,
      "value": "io.eventsourcingdb.library.book-borrowed"
    }
  }
}