When you’re using PostgreSQL together with Slick, chances are high, that you’re also using the Slick-PG library. You probably came to this post, because you try to map your custom ADT to a List/Sequence of that and want to store it as a text[] (or other array) in PostgreSQL. When trying to do so, the compiler gave you an error like:

could not find implicit value for parameter tt: slick.ast.TypedType[List[xxx.UseCase]]

You already tried creating a MappedColumnType[UseCase, String], but for some reason, Slick hasn’t picked it up / is not using it for Sequences / Lists.

Go no further, the solution is near!

Simply create a new JdbcType[List[YourType]] based on the SimpleArrayJdbcType[String] and then use the mapTo[YourType] method.

I hope you found this helpful!