It may be worth looking at qmetaobject[0] which lets you use Qt/QML from Rust. Whatever you can do in QML you can do with qmetaobject, and writing new Qt stuff can be done with some annotated Rust code. I'm using it in a personal project and quite enjoying it, the lack of C++ tooling is a joy not to be understated. I believe it's from the same author as Slint.
Although the study isn't about the FODMAPs generally, note that fructose itself is also a FODMAP (when present in larger quantities than glucose), and so could also cause similar symptoms.
EJDB [0] is pretty good and seems to be actively developed again after a period of inactivity. It uses BSON rather than JSON directly but close enough, and the queries are modelled after Mongo too.
I made a C++14 wrapper [1] a while ago which will probably still work unless EJDB itself had some drastic API changes. (I also have a C++14/1y BSON/JSON library [2] that's handy for working with EJDB, but is a bit of a playground for template metaprogramming so compile times will explode with certain functionality).
The main problem with EJDB is that it's not crash tolerant so you need signal handlers to attempt a graceful flush/close on a global handle.
I took a look at EJDB recently and thought it looked like a pretty neat project. One potential gotcha is that it is built on TokyoCabinet which AFAIK is no longer maintained. Looks like they have plans to build a v2, though.
