/**
* we look for keys that are preserved by the projection and if so these keys are the new keys,
* otherwise the 'on' attributes form the new key (key of the projection)
*/
@Override
public Keys lazyComputeKey() {
Keys keys = operand.getKeys();
Predicate<Key> p = (k) -> isKeyPreserving(k);
Set<Key> kept = keys.stream().filter(p).collect(Collectors.toSet());
if (kept.isEmpty()) {
return new Keys(type.getLargestKey());
} else {
return new Keys(kept);
}
}
