precondition-unknown

• Route: write-events
• Description: precondition type is unknown: expected 'isSubjectPristine', 'isSubjectPopulated', 'isSubjectOnEventId', or 'isEventQlQueryTrue'
• Details: precondition, the place of the precondition in its list, counting from 0, and value, the type as the request gave it.

Why It Happens#

EventSourcingDB knows four types of preconditions: isSubjectPristine, isSubjectPopulated, isSubjectOnEventId, and isEventQlQueryTrue, and refuses any other. The types are case-sensitive, so a typo such as isSubjectOnEventID, with a capital D, is enough.

Since a type that does not exist says nothing about its payload, the payload is not checked: a mistake in it shows only once the type is right. The fields of the precondition itself are checked, though, since every precondition has the same two, type and payload: a further field, such as note, and one that spells either of them otherwise, such as TYPE, are rejected with 400 Bad Request as unknown fields, whatever the type, as in /preconditions/0/TYPE: unknown field. A precondition that leaves out its type is reported as precondition-type-missing instead.

How to Fix It#

Correct the type that value shows to one of the four types, spelled exactly as they are. Sending the same request again fails the same way, since the error depends on the request alone.

Example#

For a write whose second precondition has the type isSubjectOnEventID, 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/precondition-unknown",
    "description": "precondition type is unknown: expected 'isSubjectPristine', 'isSubjectPopulated', 'isSubjectOnEventId', or 'isEventQlQueryTrue'",
    "details": {
      "precondition": 1,
      "value": "isSubjectOnEventID"
    }
  }
}