在Scala Spark应用程序中初始化SQLContext后，为什么要导入隐式SqlContext.implicits._ [英] Why import implicit SqlContext.implicits._ after initializing SQLContext in a scala spark application

问题描述

为什么要在scala spark应用程序中初始化SQLContext后导入隐式SqlContext.implicits ._.

Why import implicit SqlContext.implicits._ after initializing SQLContext in a scala spark application.

将导入放置在对象之外时，似乎有问题.

when import is put outside the object , there seems to be an issue.

我来自java的背景，不了解def对象中import语句的用法.

I am from a java back ground , where am not understanding the usage of import statements within a def object.

val sqlContext = new SQLContext(sc)

import sqlContext.implicits._
import sqlContext._

推荐答案

由于

The import doesn't work externally because the implicits object is defined inside the SQLContext class:

* :: Experimental ::
* (Scala-specific) Implicit methods available in Scala for converting
* common Scala objects into `DataFrame`s.
*
* {{{
*   val sqlContext = new SQLContext(sc)
*   import sqlContext.implicits._
* }}}
@Experimental
@InterfaceStability.Evolving
object implicits extends SQLImplicits with Serializable {
  protected override def _sqlContext: SQLContext = self
}

因此，只有拥有 SQLContext 的实例后，才能导入包含所有隐式对象的内部对象定义.

Thus, only once you have an instance of SQLContext can you import the internal object definition containing all the implicits.

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