Mapping hierarchical data in to SOLR

Experiments with Solr 4.0 (beta)

While modeling hierarchical data in XML easy, (for example org charts, Bill of materials structures) mapping to a persistent storage is very challenging. Relational SQL manages it however fetching/ updating the hierarchies is very difficult. Even books are written on mapping Tree/Graphs in to RDBMS world.

Consider simple hierarchy list looks like this:
Satya
Saketh
Dhanvi
Venkata
Dhasa

The most common and familiar known method is adjacency model, and it usually works as every node knows the adjacency node. (In SOLR world, ID contains in the unique value & parent field contains parent. Assume for the root node it is null or same.)

In SOLR each row is a document:

SOLRID Name Parent
01 Satya NULL
02 Saketh 01
03 Dhanvi 01
04 Venkata 01
05 Dhasa 04

Latest SOLR(4.0 beta?) Join functionality gives you the full hierarchy (or any piece of it) very quickly and easily.

Example queries:

1) Give me complete hierarchical list: q= {!join from=id to=parent}id:*
2) Give me immediate childs of Satya: q={!join from=id to=parent}id:Satya