At a previous company I worked at, we built a relational algebra to do server side data jobs and manipulation on NoSql style data calls. It was surprisingly effective. I proposed it at first figuring "ah it's not SQL, the team won't like it " but it was quickly adopted and proved very valuable for a couple of years. That was despite the lack of flexible enough generics and before even the Java 8 lambdas. The biggest downside was younger devs who didn't have the experience to think in data first approaches (initially at least!). I kinda regretted not making more effort to train them how to utilize relational algebra and all the flexibility it brings, even in Java.

it'll be interesting to see if this project gains traction!