title: Why can't IDEA find toDS() and toDF() functions?
body: <p>My code works well in spark-shell:</p>
  
  <pre><code>scala&gt; case class Person(name:String,age:Int)
  defined class Person
  
  scala&gt; val person = Seq(Person("ppopo",23)).toDS()
  person: org.apache.spark.sql.Dataset[Person] = [name: string, age: int]
  
  scala&gt; person.show()
  +-----+---+
  | name|age|
  +-----+---+
  |ppopo| 23|
  +-----+---+
  </code></pre>
  
  <p>but wrong in IDEA:</p>
  
  <p><a href="https://i.stack.imgur.com/2wDnH.png" rel="noreferrer"><img src="https://i.stack.imgur.com/2wDnH.png" alt="enter image description here"></a>
  <br>
  I have imported all jars in "spark-2.0.0-bin-hadoop2.7/jars/",but still can't find this function.</p>