对于相同的模块，在“ dependsOn”之后使用“ aggregate”是否多余？

TL;博士 aggregate使任务到聚合模块和所有中执行aggregated之一，而dependsOn集的CLASSPATH依赖这样的库对可见aggregateING模块（取决于是配置compile又名default中的例子）。

展示差异的样本。

我正在使用以下内容build.sbt（没有什么真正有趣的）：

lazy val a = project

lazy val b = project

lazy val c = project dependsOn b aggregate (a,b)

构建定义了三个模块a，b以及c与最后c项目是聚集a和b。第四个模块是一个隐式模块a，它汇总了所有模块b，和c。

> projects
[info] In file:/Users/jacek/sandbox/aggregate-dependsOn/
[info]     a
[info]   * aggregate-dependson
[info]     b
[info]     c

当我在aggreateing模块中执行任务时，该任务将在aggregated模块中执行。

> compile
[info] Updating {file:/Users/jacek/sandbox/aggregate-dependsOn/}b...
[info] Updating {file:/Users/jacek/sandbox/aggregate-dependsOn/}a...
[info] Updating {file:/Users/jacek/sandbox/aggregate-dependsOn/}aggregate-dependson...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Updating {file:/Users/jacek/sandbox/aggregate-dependsOn/}c...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[success] Total time: 0 s, completed Oct 22, 2014 9:33:20 AM

当我执行任务时会发生同样的情况，而任务c又会针对a和b而不是在顶级项目中执行。

> show c/clean
[info] a/*:clean
[info]  ()
[info] b/*:clean
[info]  ()
[info] c/*:clean
[info]  ()
[success] Total time: 0 s, completed Oct 22, 2014 9:34:26 AM

在a或中执行任务时b，它仅在项目内运行。

> show a/clean
[info] ()
[success] Total time: 0 s, completed Oct 22, 2014 9:34:43 AM

任务是否在aggregate项目中执行是由aggregate范围为项目和/或任务的键控制的。

> show aggregate
[info] a/*:aggregate
[info]  true
[info] b/*:aggregate
[info]  true
[info] c/*:aggregate
[info]  true
[info] aggregate-dependson/*:aggregate
[info]  true

如汇总所述更改它：

在这种情况下，在进行聚合的项目（即根项目）中，您可以控制每个任务的聚合。（...）aggregate inupdate是作用于更新任务的聚合键。

下面，我更改了c模块和clean任务的键，因此clean不再在aggregated模块a和中执行b：

> set aggregate in (c, clean) := false
[info] Defining c/*:clean::aggregate
[info] The new value will be used by no settings or tasks.
[info] Reapplying settings...
[info] Set current project to aggregate-dependson (in build file:/Users/jacek/sandbox/aggregate-dependsOn/)
> show c/clean
[info] ()
[success] Total time: 0 s, completed Oct 22, 2014 9:39:13 AM

的其他任务c不受影响，仍在执行任务c的aggregate模块中将运行该任务：

> show c/libraryDependencies
[info] a/*:libraryDependencies
[info]  List(org.scala-lang:scala-library:2.10.4)
[info] b/*:libraryDependencies
[info]  List(org.scala-lang:scala-library:2.10.4)
[info] c/*:libraryDependencies
[info]  List(org.scala-lang:scala-library:2.10.4)

虽然aggregate为sbt任务设置了一个依赖关系，以便它们在其他aggregated模块中执行，但dependsOn设置了CLASSPATH依赖关系，即dependsOned模块中的代码在一个中可见dependsOn（对不起“新”字）。

假设b有一个主要对象如下：

object Hello extends App {
  println("Hello from B")
}

将Hello对象保存到b/hello.scala，即在b模块下。

由于c已定义为dependsOn b（参见build.sbt上文），因此该Hello对象在中可见b（因为它属于模块），但在中也是可见的c。

> b/run
[info] Running Hello
Hello from B
[success] Total time: 0 s, completed Oct 22, 2014 9:46:44 AM
> c/runMain Hello
[info] Running Hello
Hello from B
[success] Total time: 0 s, completed Oct 22, 2014 9:46:58 AM

（我不得不使用runMain在c作为run单独看不到类，我无法解释）。

由于该类在模块中不可见，因此a最终尝试运行该任务。java.lang.ClassNotFoundException: Hello

> a/runMain Hello
[info] Updating {file:/Users/jacek/sandbox/aggregate-dependsOn/}a...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Running Hello
[error] (run-main-6) java.lang.ClassNotFoundException: Hello
java.lang.ClassNotFoundException: Hello
    at java.lang.ClassLoader.findClass(ClassLoader.java:530)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
[trace] Stack trace suppressed: run last a/compile:runMain for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
    at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last a/compile:runMain for the full output.
[error] (a/compile:runMain) Nonzero exit code: 1
[error] Total time: 0 s, completed Oct 22, 2014 9:48:15 AM

重新定义a为dependsOn bin build.sbt，异常消失。

您应该阅读官方文档中的多项目构建。