在不断的前pressions使用Scala常数 [英] Using scala constants in constant expressions

问题描述

我有常量，这是由其他较小的常量。例如：

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
}

我想这是真的，因为常在我的注释中使用它们。

I want these to be true constants because I use them in annotations.

我如何工作的呢？ （在斯卡拉2.11）

How do I make it work? (on scala 2.11)

我要的是

interface MyConstants {
    String TABLENAME = "table_name";
    String FIELDNAME = "field_name";
    String INDEXNAME = TABLENAME + "_" + FIELDNAME + "_ix";
}

但在阶。 Scalac不拿起使用常数标注，如果它与Java类/接口编译它们（看SI-5333 ），所以我决定把它们放在一阶对象。它适用于文字，和前pressions用文字，而不是与其他常量前pressions。

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.

有了这个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 {
}

我得到线以下错误 =指数...

标注的参数必须是一个常数;发现：MyConstants.INDEXNAME

annotation argument needs to be a constant; found: MyConstants.INDEXNAME

编辑：
的摆弄周围有几个版本的配置后，我觉得这其实是一个斯卡拉的IDE具体问题。当我建项目，或gradle这个SBT的code确实编译好的。我使用的构建工具为我的实际项目，所以它是关于在IDE中有几个INCOM prehensible标记结束 - 烦人，但有一点做与功能的

推荐答案

我用常数JPA使用Scala。这code编译，我用它：

I used constants in JPA with scala. This code compiles, and I used it:

的 FreeDays.scala 的

@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 = _
}

的 JpaQueries.scala 的

object JpaQueries extends JpaQueries

sealed trait JpaQueries {
  final val IS_FREE_DAYS = "IS_FREE_DAYS"
  final val DATE = "date"
}

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