private long countChildren(final Key parentKey) {
        final ItemsImpl items = childMap.get(parentKey);
        if (items == null) {
            return 0;
        }
        final List<ItemImpl> list = items.copy();
        // FIXME : NOTE THIS COUNT IS NOT FILTERED BY THE MAPPER.
        return list.size();
    }
Add some values to the data store.

@param values The values to add to the store.
stroom-query/stroom-query-common/src/main/java/stroom/query/common/v2/MapDataStore.java