evolve method

@override Future<void> evolve(DVCaptureSchemaChange change)

Adds or removes columns. Must be idempotent: a crash after it and before the checkpoint delivers it again.

Implementation

@override
Future<void> evolve(DVCaptureSchemaChange change) async {
  for (final String field in change.columns) {
    _checkField(field);
  }
  if (change.phase == DVCaptureSchemaPhase.expand) {
    // Added now when the type is declared; otherwise the first value
    // decides, and the field is added with it.
    await _ensureModel(change.model, <String, DVFieldType>{
      if (fieldType != null)
        for (final String field in change.columns)
          field: fieldType!(change.model, field),
    });
    return;
  }
  // A store has no column to drop, so what the source no longer declares
  // is removed from every copy instead: its values, which is what a
  // dropped column took with it. A field that became sensitive leaves the
  // destination this way too.
  await _ensureModel(change.model, <String, DVFieldType>{
    for (final String field in change.columns)
      if (!(_fields[change.model]?.containsKey(field) ?? false))
        field: DVFieldType.text,
  });
  for (final String field in change.columns) {
    await _records.update(
      change.model,
      <String, Object?>{field: null},
      where: DVFilter.isNotNull(field),
    );
  }
}