Comment by tgv

My application's primary task is to move JSON objects between storage and front-end. It does a lot more, but that's it's primary task. So document storage is a logical choice. There are no real reasons to join records, although it sometimes is more efficient to do so. MongoDB's join operation has one advantage (for 1:N relations): it groups the joined records as an array in the document, instead of multiplying the answers, so whatever function operates on the original data, also works on the joined data. The data itself is hierarchical in nature, so back-end operations also preferably work on structured data instead of rows.

You can argue that you can imitate that in Postgres or even SQLite by storing in JSON fields, but there are things they can't do quite as efficiently (e.g. indexing array contents); storage itself isn't very efficient either. But ignoring that, there's no functional difference: it's document in, document out. So then the choice boils down to speed, memory usage, etc. One day I'm going to check if Postgresql offers a real performance advantage, but given the backlog, that may take a while. Until then, MongoDB just works.