dispatchBatch<K extends Object, V> function

void dispatchBatch<K extends Object, V>(DataLoader<K, V, Object?> loader, _Batch<K, V> batch)

Implementation

void dispatchBatch<K extends Object, V>(
  DataLoader<K, V, Object?> loader,
  _Batch<K, V> batch,
) {
  // Mark this batch as having been dispatched.
  batch.hasDispatched = true;

  // If there's nothing to load, resolve any cache hits and return early.
  if (batch.keys.isEmpty) {
    _resolveCacheHits(batch);
    return;
  }

  // Call the provided batchLoadFn for this loader with the batch's keys and
  // with the loader as the `this` context.
  final batchFuture = loader._batchLoadFn(batch.keys);

  // Await the resolution of the call to batchLoadFn.
  batchFuture.then((values) {
    if (values.length != batch.keys.length) {
      throw StateError(
          'DataLoader must be constructed with a function which accepts '
          'List<key> and returns Future<List<value>>, but the function did '
          'not return a Future of an List of the same length as the List '
          'of keys.'
          '\n\nKeys:\n${batch.keys}'
          '\n\nValues:\n$values');
    }

    // Resolve all cache hits in the same micro-task as freshly loaded values.
    _resolveCacheHits(batch);

    // Step through values, resolving or rejecting each Future in the batch.
    for (var i = 0; i < batch.callbacks.length; i++) {
      final value = values[i];
      batch.callbacks[i].complete(value);
    }
  }).catchError((Object error, StackTrace stackTrace) {
    _failedDispatch(loader, batch, error, stackTrace);
  });
}