SBT Chain Task and LastModified

A short post on how you might add your task to preform in chain with other tasks.

plugins doc

Previously there was a post on testing. Being able to automatically test code you write, especially if you are still learning, will definitely make up for time spent writing tests.

Keys And Basics

Key can be defined as one of 3 different types:

1. SettingsKey on load

2. TaskKey on call

3. InputKey on call with arguments

Shorthand way to define them

TaskKey[Unit]("callTask") := {
  println("doing something here")
}

Define a key separately from the task initialization.

lazy val someTask = taskKey[Unit]("task description")

someTask <<= taskDef

private def taskDef: Def.Initialize[Task[Unit]] = Def.task {
  println("doing something here")
}

Tasks return values

TaskKey[Unit]("callTask") := {
  2
}

Chain tasks

Values are resolved as soon as they enter the scope. To make a task depend on another task use Def.taskDyn

def superTask = Def.taskDyn{
  if (shouldIcontinue.value) {
    Def.task {
      theContinuation.value
    }
  } else Def.task{}
}

Make a db and upgrade ahead of the tests

Find a file defining your model. Should be placed in watch so the modification could trigger the task recall.

val curr = 
watchSources
  .value
  .seq
  .find(
    _.getName
    .contains("model.sql"))
    .headOption
    .foreach{
  f => if (System.currentTimeMillis() - f.lastModified() < 9999)
            createDB()
}