public override DocComparator GetComparator(IndexReader reader, int docbase)
{
if (!reader.GetType().Equals(typeof(BoboIndexReader)))
throw new ArgumentException("reader must be instance of BoboIndexReader");
BoboIndexReader boboReader = (BoboIndexReader)reader;
MultiValueFacetDataCache dataCache = (MultiValueFacetDataCache)cacheBuilder.Build(boboReader);
return new MultiFacetDocComparator(dataCache);
}