Scala 中的嵌套字符串插值

Question

我正在 RDBMS 上执行查询并获取字符串形式的结果。字符串看起来像这样：

val DBASE = "my_database"
val FREQ = "monthly"
val queryResult: String = sqlContext.read.jdbc(...).collect.map(...).first
// queryResult = Database is $$${DBASE} and frequency is $$${FREQ}

接下来我将替换$$$为$，所以我留下类似的内容：

queryResult = "Database is ${DBASE} and frequency is ${FREQ}"

如何在DBASE和上使用字符串插值FREQ？我努力了：

val substituted = f"${queryResult}"

和

val substituted = s"${queryResult}"

但变量并没有被替换。除了使用以下内容之外，我还能做些什么：

queryResult.replaceAll("\\$\\{DBASE\\}", DBASE).replaceAll(...)

Answer 1

一种选择是让脚本编写模板：

     ________ ___   / /  ___  
    / __/ __// _ | / /  / _ | 
  __\ \/ /__/ __ |/ /__/ __ | 
 /____/\___/_/ |_/____/_/ | | 
                          |/  version 2.12.6

scala> import javax.script._
import javax.script._

scala> val se = new ScriptEngineManager().getEngineByName("scala")
se: javax.script.ScriptEngine = scala.tools.nsc.interpreter.Scripted@6549ce71

scala> val b = se.createBindings
b: javax.script.Bindings = javax.script.SimpleBindings@2648aa1b

scala> b.put("DBASE", "my_db")
res0: Object = null

scala> b.put("FREQ", "monthly")
res1: Object = null

scala> se.eval("""s"Db is $DBASE, freq is $FREQ"""", b)
res2: Object = Db is my_db, freq is monthly

绑定对象的类型不正确，但您可以进行强制转换或进行更多计算：

scala> se.eval("""s"Db is $DBASE, freq is ${FREQ.toString * 2}"""", b)
res4: Object = Db is my_db, freq is monthlymonthly