Scala Play making sense of a new project dependencies?

Question

I downloaded the latest activator and followed the instructions there to install it and to create a new bare-bones Play project. The new project was created successfully, however, I can't make sense of the dependencies there.

I see the generated file build.sbt containing no dependency to Play:

name := """play-template-new"""

version := "1.0-SNAPSHOT"

lazy val root = (project in file(".")).enablePlugins(PlayJava)

scalaVersion := "2.11.6"

libraryDependencies ++= Seq(
  javaJdbc,
  cache,
  javaWs
)

// Play provides two styles of routers, one expects its actions to be injected, the
// other, legacy style, accesses its actions statically.
routesGenerator := InjectedRoutesGenerator

Instead I see the sbt Play plugin being referenced under build/plugins.sbt:"

// The Play plugin
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.4.3")

// Web plugins
addSbtPlugin("com.typesafe.sbt" % "sbt-coffeescript" % "1.0.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-less" % "1.0.6")
addSbtPlugin("com.typesafe.sbt" % "sbt-jshint" % "1.0.3")
addSbtPlugin("com.typesafe.sbt" % "sbt-rjs" % "1.0.7")
addSbtPlugin("com.typesafe.sbt" % "sbt-digest" % "1.1.0")
addSbtPlugin("com.typesafe.sbt" % "sbt-mocha" % "1.1.0")

// Play enhancer - this automatically generates getters/setters for public fields
// and rewrites accessors of these fields to use the getters/setters. Remove this
// plugin if you prefer not to have this feature, or disable on a per project
// basis using disablePlugins(PlayEnhancer) in your build.sbt
addSbtPlugin("com.typesafe.sbt" % "sbt-play-enhancer" % "1.1.0")

// Play Ebean support, to enable, uncomment this line, and enable in your build.sbt using
// enablePlugins(SbtEbean). Note, uncommenting this line will automatically bring in
// Play enhancer, regardless of whether the line above is commented out or not.
// addSbtPlugin("com.typesafe.sbt" % "sbt-play-ebean" % "1.0.0")

Why are sbt plugins employed and not proper dependencies? How can I add new dependencies e.g. to Slick latest version?

Answer 1

The play sbt-plugin adds library dependencies to play framework. Just by using the plugin, all necessary dependencies are pulled in. You can check how it's done in the source-code of sbt-plugin.

As for adding slick dependency, just add following to your build.sbt file in a normal sbt way as described in getting started.

libraryDependencies ++= Seq(
  "com.typesafe.slick" %% "slick" % "2.1.0",
  "org.slf4j" % "slf4j-nop" % "1.6.4"
)