Can not create a multi project build - scala

Question

I am trying to create a Play application with a back end and a front end(using Scala.js). I separated the code into client and server folders.
For creating a Multi Project Build I looked at this http://www.scala-sbt.org/release/docs/Multi-Project.html and make my build.sbt like this:
name := """ScalaWeb"""
version := "1.0-SNAPSHOT"
lazy val commonSettings = Seq(
scalaVersion := "2.11.7",
libraryDependencies ++= Seq(
jdbc,
cache,
ws,
specs2 % Test
),
libraryDependencies ++= Seq(
"org.sorm-framework" % "sorm" % "0.3.19",
"org.scala-lang" % "scala-compiler" % scalaVersion.value force(),
"com.h2database" % "h2" % "1.3.148"
),
libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.1.0",
/*libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.1.0",
libraryDependencies += "org.slf4j" % "slf4j-api" % "1.7.12"
libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.1.3"*/
resolvers += "scalaz-bintray" at "http://dl.bintray.com/scalaz/releases",
// Play provides two styles of routers, one expects its actions to be injected, the
// other, legacy style, accesses its actions statically.
routesGenerator := InjectedRoutesGenerator,
scalacOptions += "-Ylog-classpath",
// use this if you just want jawn's parser, and will implement your own facade
libraryDependencies += "org.spire-math" %% "jawn-parser" % "0.8.3",
// use this if you want jawn's parser and also jawn's ast
libraryDependencies += "org.spire-math" %% "jawn-ast" % "0.8.3",
//for reading Json libraries
libraryDependencies += "org.scalaj" %% "scalaj-http" % "2.2.1"
)
lazy val server = (project in file("server")).settings(
commonSettings: _*
).enablePlugins(PlayScala)
lazy val client = (project in file("client")).settings(
commonSettings: _*
).enablePlugins(PlayScala)
fork in run := true
So basically I placed all dependencies into commonSettings and the imported that into the client and server projects.
However, I am getting this error:
[error] (scalaweb/compile:backgroundRun) No main class detected.
Why is this occuring?
Have I set up my build.sbt incorrectly?

Answer 1

That's because your root project (scalaweb) doesn't have a main class.
You can either:
run server's run command by doing: server/run
aggregate client and server under root project
(http://www.scala-sbt.org/0.13/docs/Multi-Project.html#Aggregation)
This might do what you wish.