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如何在writeStream中访问ArrayType中的元素?

structure streaming apache-spark scala

user9404403 · 技术社区 · 6 年前

我正在建立一个模式来接受一些数据流。它有一个包含一些元素的ArrayType。以下是我的StructType和ArrayType:

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)

这将构建一个类似“的架构”

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)

我正在尝试从模式中的“value元素”中选择值,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()

我有上面的代码,但给出了一个错误。

消息:无法解析' bit.x.inputs.element.prev_out.value '给定输入列:[键、值、时间戳、分区、偏移、, 时间戳类型,主题];;

如何访问此架构中的“value”元素?

1 回复 | 直到 6 年前

Rumesh Krishnan 6 年前

如果您有这样的数据帧,首先分解,然后选择将对您有所帮助。

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|
//+-----------+