如何在 writeStream 中访问数组类型中的元素？

Question

我正在构建一个模式来接受一些数据流。它有一个包含一些元素的 ArrayType。这是我的带有 ArrayType 的 StructType：

val innerBody = StructType(
    StructField("value", LongType, false) ::
    StructField("spent", BooleanType, false) ::
    StructField("tx_index", LongType, false) :: Nil)

val prev_out = StructType(StructField("prev_out", innerBody, false) :: Nil)

val body = StructType(
StructField("inputs", ArrayType(prev_out, false), false) :: 
StructField("out", ArrayType(innerBody, false), false) :: Nill)

val schema = StructType(StructField("x",  body, false) :: Nil)

这构建了一个类似于

的模式

root
 |-- bit: struct (nullable = true)
 |    |-- x: struct (nullable = false)
 |    |    |-- inputs: array (nullable = false)
 |    |    |    |-- element: struct (containsNull = false)
 |    |    |    |    |-- prev_out: struct (nullable = false)
 |    |    |    |    |    |-- value: long (nullable = false)
 |    |    |    |    |    |-- spent: boolean (nullable = false)
 |    |    |    |    |    |-- tx_index: long (nullable = false)
 |    |    |-- out: array (nullable = false)
 |    |    |    |-- element: struct (containsNull = false)
 |    |    |    |    |-- value: long (nullable = false)
 |    |    |    |    |-- spent: boolean (nullable = false)
 |    |    |    |    |-- tx_index: long (nullable = false)

我正在尝试 select 模式中 "value element" 的值，因为它正在流入。我正在使用 writeStream 接收器。

val parsed = df.select("bit.x.inputs.element.prev_out.value")
.writeStream.format("console").start()

我有这个但是上面的代码，但是给出了一个错误。

Message: cannot resolve 'bit.x.inputs.element.prev_out.value' given input columns: [key, value, timestamp, partition, offset, timestampType, topic];;

如何访问此架构中的 "value" 元素？

Answer 1

如果你有这样的数据框，先分解然后select会帮助你。

df.printSchema()
//root
//|-- bit: struct (nullable = true)
//|    |-- x: struct (nullable = true)
//|    |    |-- inputs: array (nullable = true)
//|    |    |    |-- element: struct (containsNull = true)
//|    |    |    |    |-- prev_out: struct (nullable = true)
//|    |    |    |    |    |-- spent: boolean (nullable = true)
//|    |    |    |    |    |-- tx_infex: long (nullable = true)
//|    |    |    |    |    |-- value: long (nullable = true)

import org.apache.spark.sql.functions._
val intermediateDf: DataFrame = df.select(explode(col("bit.x.inputs")).as("interCol"))
intermediateDf.printSchema()

//root
//|-- interCol: struct (nullable = true)
//|    |-- prev_out: struct (nullable = true)
//|    |    |-- spent: boolean (nullable = true)
//|    |    |-- tx_infex: long (nullable = true)
//|    |    |-- value: long (nullable = true)

val finalDf: DataFrame = intermediateDf.select(col("interCol.prev_out.value").as("value"))
finalDf.printSchema()
//root
//|-- value: long (nullable = true)


finalDf.show()
//+-----------+
//|      value|
//+-----------+
//|12347628746|
//|12347628746|
//+-----------+

如何在 writeStream 中访问数组类型中的元素？

How to access elements in a ArrayType in a writeStream?

scala

apache-spark

streaming

structure