Subqueries

A typical case you may require is running a Query which depends on another Query result.

Start by importing:

import scalaql._

// Docs classes
import scalaql.docs.Hogwarts._

Assume you'd like to find faculties that have adult students.
This could be done via exists method:

def hasAdults(faculty: Faculty) =
  select[Student]
    .where(_.faculty == faculty.name)
    .exists(_.age >= 18)

You could apply this function (which uses a Query) on another Query via whereSubQuery:

val subSelectQuery = 
  select[Faculty]
    .whereSubQuery(hasAdults)
// subSelectQuery: Query[From[Faculty] with From[Student], Faculty] = FROM(Hogwarts::Faculty) -> WHERE SUBQUERY

Then run it:

subSelectQuery
  .show(truncate = false)
  .run(
    from(students) & from(faculties)
  )
// +----------+-----------------+---------------------+
// |name      |founder          |description          |
// +----------+-----------------+---------------------+
// |Gryffindor|Godric Gryffindor|100 points by default|
// |Slytherin |Salazar Slytherin|The bad guys         |
// +----------+-----------------+---------------------+
//