[英]How to execute a block of python code only when a row has been selected from mysql database
[英]How to execute code when no result selected using Anorm?
當存在與WHERE
子句匹配的記錄時,此代碼可以正常工作:
val pinfo = SQL("SELECT * FROM tableName WHERE id={id}").on("id" -> "scala")
pinfo().map { row =>
println("have something")// runs when selected
}
什么都沒有被選中會發生什么?
當沒有從MySQL中選擇記錄時,我想打印以下內容。
println("nothing is selected")//if no row comes
SQL(...)()
返回一個Stream[SqlRow]
,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")
也來自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
您也可以將其解析為Option[T]
,然后處理此可選結果中沒有值的情況。
val i: Option[Int] = SQL"SELECT int FROM test".as(scalar[String].singleOpt)
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.