build static method

Future<ExternalDataInstance> build(ResourceResolver resolver, String instanceSrc, String instanceId, { ExternalInstanceParser? parser, bool placeholderIfMissing = true, })

Loads the instance instanceId from instanceSrc with parser (default: ExternalInstanceParser with its CSV and GeoJSON parsers), reading files through resolver.

Instance providers are asked for a partial instance first; it's completed when evaluation reaches a partial element.

With placeholderIfMissing false a missing file throws ResourceNotFoundException instead, as JavaRosa's readExternal (deserializing a cached form) does.

Implementation

static Future<ExternalDataInstance> build(
  ResourceResolver resolver,
  String instanceSrc,
  String instanceId, {
  ExternalInstanceParser? parser,
  bool placeholderIfMissing = true,
}) async {
  final instanceParser = parser ?? ExternalInstanceParser();
  TreeElement? root;
  TreeElement Function()? reload;
  try {
    (root, reload) = await instanceParser.parseWithReload(
      resolver,
      instanceId,
      instanceSrc,
      partial: true,
    );
  } on ResourceNotFoundException {
    if (!placeholderIfMissing) rethrow;
    root = null;
  }
  final usePlaceholder = root == null || !root.hasChildren;
  return ExternalDataInstance._(
    usePlaceholder ? TreeElement(placeholderName, 0) : root,
    instanceId,
    instanceSrc,
    isUsingPlaceholder: usePlaceholder,
    reload: usePlaceholder ? null : reload,
  );
}