We went through a similar migration process and it sounds like we had different experiences. We started with the devs taking some time just to study and learn Scala basics then added the frameworks on top of that. I think if you go that way and you're using Slick > 2.0 it really starts to look like idiomatic Scala and everything in Slick looks like List manipulations. The other bonus is that a lot of the SQL generated perfors well and is easy to read.
Fair enough, thanks for the perspective!
What library would you use instead of slick?
You could try https://github.com/njeuk/dbmapper . I use this for my Scala projects, having rejecting Slick and it's unwanted data DSL.
For a large org, Slick also adds to the already significant Scala learning curve for Java devs. Scala itself is good and pretty, but when the first task you give someone new is to write a CRUD-like rest service using slick on one end, and spray on the other, they don't get to spend any time learning actual scala, and instead domain specific languages that are hard to reason about without serious Scala experience. No, this is not speculation: We are going through this problem at work right now, with dozens of developers learning Scala, and only a few of us that really started with significant experience.
If I have to use slick, I use the few direct SQL bits. From my perspective, is the one saving grace of the library.