Using scala constants in constant expressions - scala

Question

I have constants, that are made of other, smaller constants. For example
object MyConstants {
final val TABLENAME = "table_name";
final val FIELDNAME = "field_name";
final val INDEXNAME = TABLENAME + "_" + FIELDNAME + "_ix"; // this one does not want to be constant
}
I want these to be true constants because I use them in annotations.
How do I make it work? (on scala 2.11)
What I want is
interface MyConstants {
String TABLENAME = "table_name";
String FIELDNAME = "field_name";
String INDEXNAME = TABLENAME + "_" + FIELDNAME + "_ix";
}
but in scala. Scalac does not pick up constants for usage in annotations if it compiles them from java class/interface (see SI-5333) so I decided to put them in a scala object. It works for literals, and for expressions with literals, but not for expressions with other constants.
With this code:
import javax.persistence.Entity
import javax.persistence.Table
import org.hibernate.annotations.Index
object MyConstants {
final val TABLENAME = "table_name";
final val FIELDNAME = "field_name";
final val INDEXNAME = TABLENAME + "_" + FIELDNAME + "_ix";
}
#Entity
#Table(name = MyConstants.TABLENAME)
#org.hibernate.annotations.Table(
appliesTo = MyConstants.TABLENAME,
indexes = Array(new Index(name = MyConstants.INDEXNAME, columnNames = Array(MyConstants.FIELDNAME))))
class MyEntity {
}
I get a following error on line indexes = ...
annotation argument needs to be a constant; found: MyConstants.INDEXNAME
Edit:
After fiddling around with a few build configurations, I think this is actually a scala-ide specific issue. The code does indeed compile alright when I build project with gradle or sbt. I do use build tool for my actual projects, so in the end it's about having a few incomprehensible markers in the IDE - annoying, but has little to do with functionality.

Answer 1

I used constants in JPA with scala. This code compiles, and I used it:
FreeDays.scala
#Entity
#Table(name = "free_days")
#NamedQueries(
Array(
new NamedQuery(name = JpaQueries.IS_FREE_DAYS, query = "SELECT f FROM FreeDays f WHERE f.dateOfFreeDay = :" + JpaQueries.DATE)
)
)
class FreeDays {
def this(id: Int, name: String, dateOfFreeDay: Date) = {
this()
this.id = id
this.name = name
this.dateOfFreeDay = dateOfFreeDay
}
#Id
#GeneratedValue
var id: Long = _
var name: String = _
#Column(name = "date_of_free_day")
#Temporal(TemporalType.DATE)
var dateOfFreeDay: Date = _
}
JpaQueries.scala
object JpaQueries extends JpaQueries
sealed trait JpaQueries {
final val IS_FREE_DAYS = "IS_FREE_DAYS"
final val DATE = "date"
}