Scala for Data Science

Invokers

Invokers are the components of a Slick query that build up the SQL select statement. Slick exposes a variety of invokers that allow the construction of complex queries. Let's look at some of these invokers here:

• The map invoker is useful to select individual columns or apply operations to columns:

  scala> db.withSession { implicit session =>
    Tables.transactions.map {
      _.candidate 
    }.take(5).list       
  }
  List[String] = List(Obama, Barack, Paul, Ron, Paul, Ron, Paul, Ron, Obama, Barack)
  

• The filter invoker is the equivalent of the WHERE statements in SQL. Note that Slick fields must be compared using ===:

  scala> db.withSession { implicit session => 
    Tables.transactions.filter {
      _.candidate === "Obama, Barack"
    }.take(5).list
  }
  List[Tables.Transactions#TableElementType] ...