Question

进行多项目构建时，可以在dependsOn中列出您依赖的项目，并且任务将首先在依赖项上运行，因此您可以依赖于它们的结果。

还有一个aggregate任务，它聚合子项目。汇总和取决于子项目的方式有何不同？在什么情况下应使用aggregrate而不是dependsOn

Answer 1

关键区别在于aggregate不会修改 classpath ，也不会在子项目之间建立 ordering 。考虑以下由root，core和util项目组成的多项目构建：

├── build.sbt
├── core
│   ├── src
│   └── target
├── project
│   ├── build.properties
│   └── target
├── src
│   ├── main
│   └── test
├── target
│   ├── scala-2.13
│   └── streams
└── util
├── src
└── target

其中

core/src/main/scala/example/Core.scala:

package example

object Core {
  def foo = "Core.foo"
}

util/src/main/scala/example/Util.scala

package example

object Util {
  def foo =
    "Util.foo" + Core.foo // note how we depend on source from another project here
}

src/main/scala/example/Hello.scala:

package example

object Hello extends App {
  println(42)
}

请注意Util.foo项目对Core.foo的{{1}}具有类路径依赖性。如果我们现在尝试像这样使用core建立“依赖关系”

aggregate

然后从lazy val root = (project in file(".")).aggregate(core, util) lazy val util = (project in file("util")) lazy val core = (project in file("core"))项目执行compile

root

它确实会尝试编译所有聚合的项目，但是root/compile将因为缺少类路径依赖项而编译失败：

Util

查看此问题的另一种方法是执行sbt:aggregate-vs-dependsOn> root/compile [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/target/scala-2.13/classes ... [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/core/target/scala-2.13/classes ... [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/util/target/scala-2.13/classes ... [error] /Users/mario/IdeaProjects/aggregate-vs-dependson/util/src/main/scala/example/Util.scala:5:18: not found: value Core [error] "Util.foo" + Core.foo // note how we depend on source from another project here [error] ^ [error] one error found [error] (util / Compile / compileIncremental) Compilation failed [error] Total time: 1 s, completed 13-Oct-2019 12:35:51，它应该在输出中缺少show util/dependencyClasspath依赖性。

另一方面，Core将修改类路径并在项目之间建立适当的顺序

dependsOn

现在lazy val root = (project in file(".")).aggregate(core, util) lazy val util = (project in file("util")).dependsOn(core) lazy val core = (project in file("core"))给出

root/compile

和sbt:aggregate-vs-dependsOn> root/compile [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/target/scala-2.13/classes ... [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/core/target/scala-2.13/classes ... [info] Compiling 1 Scala source to /Users/mario/IdeaProjects/aggregate-vs-dependson/util/target/scala-2.13/classes ... [success] Total time: 1 s, completed 13-Oct-2019 12:40:25在类路径上显示show util/dependencyClasspath：

Core

最后，sbt:aggregate-vs-dependsOn> show util/dependencyClasspath [info] * Attributed(/Users/mario/IdeaProjects/aggregate-vs-dependson/core/target/scala-2.13/classes)和aggregate并不互斥，实际上，通常同时使用两者，通常在dependsOn上同时使用aggregate子项目以帮助构建，同时使用root为特定子项目手工制作特定订单。

你什么时候需要在dependOn上聚合

1 个答案: