Solr has added support for taking childDocs as input ( only XML till now ). It's currently used for BlockJoinQuery.
I feel that if a user indexes a document with child docs, even if he isn't using the BJQ features and is just searching which results in a hit on the parentDoc, it's childDocs should be returned in the response format.
Chris Hostetter (Unused) on IRC suggested that the DocTransformers would be the place to add childDocs to the response.
Now given a docId one needs to find out all the childDoc id's. A couple of approaches which I could think of are
1. Maintain the relation between a parentDoc and it's childDocs during indexing time in maybe a separate index?
2. Somehow emulate what happens in ToParentBlockJoinQuery.nextDoc() - Given a parentDoc it finds out all the childDocs but this requires a childScorer.
Am I missing something obvious on how to find the relation between a parentDoc and it's childDocs because none of the above solutions for this look right.