EntityReference, Solr 4.x and Join Queries

With Solr 4.x, we've been given the ability to perform join queries.

In Drupal one of the main ways of creating references between nodes is using the entityreference module.

Unfortunately due to how we're storing the entityreference fields in the index with the apachesolr module, joins are not possible.

It would be wise to change the format of how entityreferences are stored in the solr index to be the solr IDs of the documents they reference.

Currently node IDs in solr look like this "8yx3v3/node/94388" but entityreference values in documents look like this "node:94388". I doubt many people are using the entityreferences in solr

I'm going to need to perform join's on the project I'm working on (or de-normalize my data more) but it seems that it would be a good idea to create proper IDs with entityreferences so that this functionality could exist.

Here's the solr join syntax.

http://wiki.apache.org/solr/Join

I'm starting to think since Solr 4 provides many other features not provided by solr 3.x and since there's also a new solarium for Solr 4.x, that perhaps it's time to fork this project to apachesolr 2.x and get the solr 4 functionality integrated. Since Solarium 3.x is based on Symphony framework name spacing, it would help with the move to D8 as well.