从模型列表中填充下拉列表

Question

我尝试显示一个从模型中获取其选项的选择字段。

我尝试按照以下 stackoverflow 问题中的说明进行操作：

• How to prefill a dropdown using scala template and play framework
• Populate a html drop down list in play framework
• Use of option helper in Play Framework 2.0 templates

但我无法让它工作。

给定以下模型：

public class Model {
    private String field;
    private List<String> options
}

还有以下观点：

@(modelForm: Form[models.Model])

@helper.select(field = modelForm("field"), options = helper.options(modelForm("options").value()))

helper.options 的 apply 方法有一个 java.util.List[String] 条目，因此它应该可以用于 java 字符串列表。

def apply(options: java.util.List[String]) = options.asScala.map(v => v -> v)

这样我只会得到以下错误：

overloaded method value apply with alternatives:
[error]   (options: java.util.List[String])scala.collection.mutable.Buffer[(String, String)] <and>
[error]   (options: List[String])List[(String, String)] <and>
[error]   (options: java.util.Map[String,String])Seq[(String, String)] <and>
[error]   (options: Map[String,String])Seq[(String, String)] <and>
[error]   (options: (String, String)*)Seq[(String, String)]
[error]  cannot be applied to (String)
[error]             options = helper.options(modelForm("options").value())

如果我另外将表单字段转换为 java.util.List<String> 而不是编译时异常，我会得到运行时异常：

@helper.select(field = modelForm("field"), options = helper.options(modelForm("options").value().asInstanceOf[util.List[String]]))

运行时异常：

[error] ErrorHandler - Exception StackTrace: 
[views.html.modelFormView$.$anonfun$apply$1(modelFormView.template.scala:48), 
views.html.helper.form$.apply(form.template.scala:36), 
views.html.modelFormView$.apply(modelFormView.template.scala:41), 
views.html.modelFormView$.render(modelFormView.template.scala:75), 
views.html.modelFormView.render(modelFormView.template.scala), 
controllers.modelController.requestJwt(modelController.java:71), 
router.Routes$$anonfun$routes$1.$anonfun$applyOrElse$16(Routes.scala:304), 
play.core.routing.HandlerInvokerFactory$$anon$3.resultCall(HandlerInvoker.scala:134), play.core.routing.HandlerInvokerFactory$$anon$3.resultCall(HandlerInvoker.scala:133), play.core.routing.HandlerInvokerFactory$JavaActionInvokerFactory$$anon$8$$anon$2$$anon$1.invocation(HandlerInvoker.scala:108), play.core.j.JavaAction$$anon$1.call(JavaAction.scala:88), 
play.http.DefaultActionCreator$1.call(DefaultActionCreator.java:31), 
play.core.j.JavaAction.$anonfun$apply$8(JavaAction.scala:138), 
scala.concurrent.Future$.$anonfun$apply$1(Future.scala:655), 
scala.util.Success.$anonfun$map$1(Try.scala:251), 
scala.util.Success.map(Try.scala:209), 
scala.concurrent.Future.$anonfun$map$1(Future.scala:289), 
scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29), 
scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29), 
scala.concurrent.impl.CallbackRunnable.run$$$capture(Promise.scala:60), 
scala.concurrent.impl.CallbackRunnable.run(Promise.scala), 
play.core.j.HttpExecutionContext$$anon$2.run(HttpExecutionContext.scala:56), 
play.api.libs.streams.Execution$trampoline$.execute(Execution.scala:70), 
play.core.j.HttpExecutionContext.execute(HttpExecutionContext.scala:48), 
scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:68), 
scala.concurrent.impl.Promise$KeptPromise$Kept.onComplete(Promise.scala:368), 
scala.concurrent.impl.Promise$KeptPromise$Kept.onComplete$(Promise.scala:367), 
scala.concurrent.impl.Promise$KeptPromise$Successful.onComplete(Promise.scala:375), 
scala.concurrent.impl.Promise.transform(Promise.scala:29), 
scala.concurrent.impl.Promise.transform$(Promise.scala:27), 
scala.concurrent.impl.Promise$KeptPromise$Successful.transform(Promise.scala:375), 
scala.concurrent.Future.map(Future.scala:289), 
scala.concurrent.Future.map$(Future.scala:289), 
scala.concurrent.impl.Promise$KeptPromise$Successful.map(Promise.scala:375), 
scala.concurrent.Future$.apply(Future.scala:655), 
play.core.j.JavaAction.apply(JavaAction.scala:138), 
play.api.mvc.Action.$anonfun$apply$2(Action.scala:96), 
play.api.libs.streams.StrictAccumulator.$anonfun$mapFuture$4(Accumulator.scala:174), 
scala.util.Try$.apply(Try.scala:209), 
play.api.libs.streams.StrictAccumulator.$anonfun$mapFuture$3(Accumulator.scala:174), 
scala.Function1.$anonfun$andThen$1(Function1.scala:52), 
play.api.libs.streams.StrictAccumulator.run(Accumulator.scala:207), 
play.core.server.AkkaHttpServer.$anonfun$runAction$4(AkkaHttpServer.scala:304), 
akka.http.scaladsl.util.FastFuture$.strictTransform$1(FastFuture.scala:41), 
akka.http.scaladsl.util.FastFuture$.$anonfun$transformWith$3(FastFuture.scala:51), 
scala.concurrent.impl.CallbackRunnable.run$$$capture(Promise.scala:60), 
scala.concurrent.impl.CallbackRunnable.run(Promise.scala), 
akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55), 
akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:91), 
scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12), 
scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:81), 
akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:91), 
akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:40), 
akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:43), akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260), 
akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339), 
akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979), 
akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)]

我不明白我做错了什么。

Answer 1

documentation 告诉 helper.select 想要一个 Seq[(String, String)] 作为 options-argument。

在您的代码中，modelForm("options") 是对 Form 上的方法 apply(name: String) 的调用，该方法返回 Form.Field (doc)。类Form.Field 有一个方法value，但它返回一个String。

String 不是Seq[(String, String)]。

您必须将 Seq[(String, String)] 作为单独的参数传递，或者就地构造它。

Answer 2

您是否尝试过在旋转选择对象内进行映射？

@helper.select(field = modelForm("field"), options = modelForm("options").asScala.map(v => v -> v).value()))

因为这些错误：

[error]   (options: (String, String)*)Seq[(String, String)]
[error]  cannot be applied to (play.data.Form.Field)
[error]             options = helper.options(modelForm("options").value())

让我相信它并不期望在那个阶段有地图。