sbt: run task on subproject

Question

I have the following project structure:

lazy val root = project.aggregate(rest,backend)
lazy val rest = project
lazy val backend = project

When I execute the "run" task from the parent, I want a specific class from the "backend" project to have its main method executed. How would I accomplish this?

Answer 1

lazy val root = project
  .aggregate(rest, backend)
  .dependsOn(rest, backend) //<- don't forget dependsOn
lazy val rest =
  project
lazy val backend =
  project.settings(
    Compile / run / mainClass := Some("fully.qualified.path.to.MainClass")
  )

Compile / run := (backend / Compile / run).evaluated