当没有使用Anorm选择结果时如何执行代码？

Question

当存在与WHERE子句匹配的记录时,此代码可以正常工作:

val pinfo = SQL("SELECT * FROM tableName WHERE id={id}").on("id" -> "scala")
pinfo().map { row =>
  println("have something")// runs when selected
}

什么都没有被选中会发生什么？

当没有从MySQL中选择记录时,我想打印以下内容.

println("nothing is selected")//if no row comes

Answer 1

SQL(...)()返回一个Stream[SqlRow]和流有isEmpty方法:

val pinfo: Stream[SqlRow] = SQL("SELECT * FROM tableName WHERE id={id}").on("id" -> "scala")()
if(!pinfo.isEmpty) pinfo.map { row => println("have something") }
else println("nothing is selected")

也来自REPL:

scala> 1 #:: 2 #:: empty
res0: scala.collection.immutable.Stream[Int] = Stream(1, ?)

scala> res0.isEmpty
res1: Boolean = false

scala> empty
res2: scala.collection.immutable.Stream[Nothing] = Stream()

scala> res2.isEmpty
res3: Boolean = true