static KeyExtractor.Factory forMultipleMembers(Function<Class<?>, List<Member>> keyLookupFn) {
    Objects.requireNonNull(keyLookupFn, "keyLookupFn");
    return entityType -> new KeyExtractors.MultipleMembers(entityType, keyLookupFn.apply(entityType));
  }
Factory to extract composite key using multiple members of a class.

@param keyLookupFn function extracting multiple members from a entity representing composite key
criteria/common/src/org/immutables/criteria/backend/KeyExtractor.java