IRIS as a document database and Properties population

Hello all,

I'm "playing" a little bit with IRIS as document database, as it seems really simple to use.

So far, creating a database and inserting documents is fine. Creating a Property so it can be indexed seems very useful and it works well when this property is created at the very beginning. But here my "problem": whenever a new property is added, how can the values be recalculated and inserted, so indices can be correctly updated? 

So far, I've only found as a solution opening and saving the documents :'( This is ok for a POC, but what when millions of documents are stored?