Sugar class for providing basic join language

JoinDataSet.scala

class JoinDataSet[L, R](lhs: Dataset[L], rhs: Dataset[R], joinType: String)
object JoinDataSet {
  def apply[L, R](lhs: Dataset[L], rhs: Dataset[R], joinType: String) = new JoinDataSet(lhs, rhs, joinType)
  def leftJoin[L, R](lhs: Dataset[L], rhs: Dataset[R])                = JoinDataSet(lhs, rhs, "leftOuter")
  def rightJoin[L, R](lhs: Dataset[L], rhs: Dataset[R])               = JoinDataSet(lhs, rhs, "rightOuter")
  def fullOuterJoin[L, R](lhs: Dataset[L], rhs: Dataset[R])           = JoinDataSet(lhs, rhs, "fullOuter")
}