为路由中的可选查询参数指定null默认值 - Play Framework [英] assign null default value for optional query param in route - Play Framework

问题描述

我正在尝试定义一个可选的查询参数，该参数将映射到 Long ，但是 null 当它不在URL中时：

I'm trying to define an optional query parameter that will map to a Long, but will be null when it is not present in the URL:

GET  /foo  controller.Foo.index(id: Long ?= null)

...我基本上想检查是否传入：

... and I essentially want to check if it was passed in or not:

public static Result index(Long id) {
    if (id == null) {...}
    ...
}

但是，我收到编译错误：

However, I'm getting a compilation error:

类型不匹配; found：Null（null）required：Long请注意，隐式
转换不适用，因为它们不明确：两个方法
类LowPriorityImplicits中的Long2longNullConflict类型（x：
Null）Long和方法Long2long in object Predef of type（x：Long）Long
是可能的转换函数，从Null（null）到Long

type mismatch; found : Null(null) required: Long Note that implicit conversions are not applicable because they are ambiguous: both method Long2longNullConflict in class LowPriorityImplicits of type (x: Null)Long and method Long2long in object Predef of type (x: Long)Long are possible conversion functions from Null(null) to Long

为什么我不能这样做，将 null 指定为预期 Long 可选查询参数的默认值？有什么方法可以做到这一点？

Why can't I do this, assigning null to be a default value for an expected Long optional query parameter? What's an alternative way to do this?

推荐答案

请记住路线中的可选查询参数类型为 scala.Long ，而不是 java.lang.Long 。 Scala的Long类型相当于Java的原始 long ，并且不能赋值为 null 。

Remember that the optional query parameter in your route is of type scala.Long, not java.lang.Long. Scala's Long type is equivalent to Java's primitive long, and cannot be assigned a value of null.

将 id 更改为 java.lang.Long 类型应修复编译错误，也许是解决问题的最简单方法：

Changing id to be of type java.lang.Long should fix the compilation error, and is perhaps the simplest way to resolve your issue:

GET  /foo  controller.Foo.index(id: java.lang.Long ?= null)

你也可以尝试包装 id 在Scala 选项中，因为这是Scala处理可选值的推荐方法。但是我不认为Play会将可选的Scala Long映射到可选的Java Long（反之亦然）。您要么必须在路线中使用Java类型：

You could also try wrapping id in a Scala Option, seeing as this is the recommended way in Scala of handling optional values. However I don't think that Play will map an optional Scala Long to an optional Java Long (or vice versa). You'll either have to have a Java type in your route:

GET  /foo  controller.Foo.index(id: Option[java.lang.Long])

public static Result index(final Option<Long> id) {
    if (!id.isDefined()) {...}
    ...
}

或Java代码中的Scala类型：

Or a Scala type in your Java code:

GET  /foo  controller.Foo.index(id: Option[Long])

public static Result index(final Option<scala.Long> id) {
    if (!id.isDefined()) {...}
    ...
}

这篇关于为路由中的可选查询参数指定null默认值 - Play Framework的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！