无法从Build.scala访问项目的类/对象 [英] Can't get access to a project's classes / objects from Build.scala

问题描述

我想创建像Ruby rake这样的任务.我知道我可以通过sbt任务完成 http://www.scala-sbt .org/release/docs/Detailed-Topics/Tasks 但我不能使用项目中的任何类或对象.例如:

I'd like to create the task like Ruby rake. I know I can do by sbt tasks http://www.scala-sbt.org/release/docs/Detailed-Topics/Tasks But I can't use any class or object from my project. For example:

# project/AppBuild.scala
object AppBuild extends Build {
  //............
    lazy val sampleTask = taskKey[Unit]("hello123", "A sample task.") := {
      val u = models.User.single(123) // Error! models is not accessible
    }

}

所以我无法访问model.User或项目中的任何其他类.我该怎么办?

So I can't get access to models.User or any other class in my project. What can I do about this?

推荐答案

Scala是强类型的，所有类型都必须在编译时解析.您的构建文件是先编译的-它不能依赖于它正在构建的项目的类型，因为要构建它正在构建的项目，它首先需要自己构建-看到循环依赖吗?

Scala is strongly typed, all types must be resolved at compile time. Your build file is first compiled - it can't depend on types from the project it's building since to build the project it is building it first needs to be built itself - see the circular dependency?

因此，您不能简单地从构建文件中调用项目中的Scala代码.

So you can't simply call Scala code in your project from your build file.

您可以做的是在项目中定义一个主类，并告诉SBT使用runMain任务来调用它.这完成了首先编译项目，然后创建具有所有必要依赖项的类加载器，然后反射性地查找主类并调用它的所有魔术.请注意，大概您的代码需要一个正在运行的应用程序，因此最好在test文件夹中执行此操作，并使用Play的伪造应用程序帮助程序，例如:

What you can do is define a main class in your project, and tell SBT to invoke that using the runMain task. This does all the magic necessary to first compile your project, then create a classloader with all the necessary dependencies, then lookup your main class reflectively and invoke it. Note that presumably your code needs a running application, so you'll be best off to do this in the test folder and use Play's fake application helper, eg:

package foo.bar

import play.api.test._
object MyMainClass extends App {
  Helpers.running(FakeApplication()) {
    val u = models.User.single(123)
    ...
  }
}

现在从play控制台中尝试以下操作:

Now from the play console, try this:

test:runMain foo.bar.MyMainClass

如果可行，则可以通过将其添加到build.sbt或在Build.scala中建立设置来缩短它:

If that works, then you can shorten it by adding this to your build.sbt or build settings in Build.scala:

TaskKey[Unit]("do-something", "Do something") := {
  (runMain in Test).toTask("foo.bar.MyMainClass").value
}

那么您应该只能够运行do-something.

Then you should just be able to run do-something.

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