在 Scala 中使用 JDOQL 结果

发布于 2024-07-30 03:48:37 字数 460 浏览 4 评论 0原文

我正在尝试将 JDO 与 Google App Engine 和 Scala 一起使用。执行的 api 返回 Object （但它实际上是一个 java 集合），我想将它放入 scala 列表中以对其进行迭代。

到目前为止，我的代码如下所示：

val pm = PMF.factory.getPersistenceManager
val query = "select from User " 
val gamelist:List[User] = List(pm.newQuery(query).execute.toArray:_ *)

此时的编译错误是 toArray 不是 Object 的成员。执行上述操作的最佳方法是什么？我尝试使用 .asInstanceOf[java.util.Collection[User]]，但这是一次失败的尝试。

原文

I'm trying to use a JDO with Google App Engine and Scala. The api for the execute returns Object (but it's really a java collection) and I want to get it into a scala list to iterate over it.

My code looks like this so far:

val pm = PMF.factory.getPersistenceManager
val query = "select from User " 
val gamelist:List[User] = List(pm.newQuery(query).execute.toArray:_ *)

The compile error at this point is toArray is not a member of Object. What is the best way to do the above? I tried to use .asInstanceOf[java.util.Collection[User]], but it was a failed attempt.

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您的好友蓝忘机已上羡 2024-08-06 03:48:37

使用 scala.collection.jcl.Conversions：

import scala.collection.jcl.Conversions._
...
// this gets you a List[User]
val gameList = pm.newQuery(query).execute.asInstanceOf[java.util.List[User]].toList
...
// or you can just iterate through the return value without converting it to List
pm.newQuery(query).execute.asInstanceOf[java.util.List[User]] foreach (println(_))

Use scala.collection.jcl.Conversions:

import scala.collection.jcl.Conversions._
...
// this gets you a List[User]
val gameList = pm.newQuery(query).execute.asInstanceOf[java.util.List[User]].toList
...
// or you can just iterate through the return value without converting it to List
pm.newQuery(query).execute.asInstanceOf[java.util.List[User]] foreach (println(_))

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硬不硬你别怂 2024-08-06 03:48:37

问题是 Java 集合不是 scala 集合。您需要 jcl 包中的隐式转换：

import collections.jcl.Conversions._
import java.util.{Collection => JCollection}

val pm = PMF.factory.getPersistenceManager
val query = "select from User " 

val users = pm.newQuery(query).execute.asInstanceOf[JCollection[User]]
val gamelist:List[User] = List(users.toArray: _*) //implicit conversion here

The problem is that the Java collection is not a scala collection. Youy need the implicit conversions in the jcl package:

import collections.jcl.Conversions._
import java.util.{Collection => JCollection}

val pm = PMF.factory.getPersistenceManager
val query = "select from User " 

val users = pm.newQuery(query).execute.asInstanceOf[JCollection[User]]
val gamelist:List[User] = List(users.toArray: _*) //implicit conversion here

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