Hierarchical Facets

[Andrew Nagy]

I am running into a stumbling block and can only find a way to solve the 
problem with some sort of hierarchical faceting system.  I am in the 
process of moving my records from eXist (http://exist.sf.net) to Solr, 
but the problem is with the lack of a "directory structure" that exist 
has.  I figure I could easily solve this problem by setting a field 
called "collection" and then faceting on that field to get my list of 
"directories" however this will not allow me to do subdirectories.

Any ideas on how to implement such a thing in solr?
Thanks!
Andrew