batch
suspend fun <T : NodeObject, C : SelectiveNodeExecutionContext<T>, K> batchByCustomGrouping(contexts: List<C>, groupBy: (SelectionSet<T>) -> K, resolve: suspend (Group<T, C, K>) -> Map<C, FieldValue<T>>): Map<C, FieldValue<T>>(source)
Partitions contexts by a tenant-defined key derived from each context's selection set.
Group.contexts keeps the input order.
Blocks for different groups may run concurrently, so resolve should not mutate shared state.
resolve should return a value for every context in its group. If it leaves one out, that context is missing from the result and Viaduct fails the whole batch.
If a block throws an exception or times out, every context in its group gets an error. Other groups are not affected.
If the caller is cancelled or groupBy throws, the whole call fails.