mysql - 使用 Anorm 没有选择结果时如何执行代码？

Question

当有记录匹配 WHERE 子句时，这段代码工作正常:

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

什么都没有选择时会发生什么？

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] 并且流有 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")

同样来自 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