[英]Why is "Unable to find encoder for type stored in a Dataset" when creating a dataset of custom case class?
[英]Why is the error “Unable to find encoder for type stored in a Dataset” when encoding JSON using case classes?
我寫過火花工作:
object SimpleApp {
def main(args: Array[String]) {
val conf = new SparkConf().setAppName("Simple Application").setMaster("local")
val sc = new SparkContext(conf)
val ctx = new org.apache.spark.sql.SQLContext(sc)
import ctx.implicits._
case class Person(age: Long, city: String, id: String, lname: String, name: String, sex: String)
case class Person2(name: String, age: Long, city: String)
val persons = ctx.read.json("/tmp/persons.json").as[Person]
persons.printSchema()
}
}
在IDE中運行main函數時,發生2錯誤:
Error:(15, 67) Unable to find encoder for type stored in a Dataset. Primitive types (Int, String, etc) and Product types (case classes) are supported by importing sqlContext.implicits._ Support for serializing other types will be added in future releases.
val persons = ctx.read.json("/tmp/persons.json").as[Person]
^
Error:(15, 67) not enough arguments for method as: (implicit evidence$1: org.apache.spark.sql.Encoder[Person])org.apache.spark.sql.Dataset[Person].
Unspecified value parameter evidence$1.
val persons = ctx.read.json("/tmp/persons.json").as[Person]
^
但是在Spark Shell中,我可以毫無錯誤地運行這個作業。 問題是什么?
錯誤消息表明Encoder
無法接受Person
案例類。
Error:(15, 67) Unable to find encoder for type stored in a Dataset. Primitive types (Int, String, etc) and Product types (case classes) are supported by importing sqlContext.implicits._ Support for serializing other types will be added in future releases.
將case類的聲明SimpleApp
的范圍之外。
如果添加你有同樣的錯誤sqlContext.implicits._
和spark.implicits._
在SimpleApp
(順序並不重要)。
刪除一個或另一個將是解決方案:
val spark = SparkSession
.builder()
.getOrCreate()
val sqlContext = spark.sqlContext
import sqlContext.implicits._ //sqlContext OR spark implicits
//import spark.implicits._ //sqlContext OR spark implicits
case class Person(age: Long, city: String)
val persons = ctx.read.json("/tmp/persons.json").as[Person]
使用Spark 2.1.0進行測試
有趣的是,如果你添加兩個相同的對象,你就不會有問題。
@Milad Khajavi
在對象SimpleApp之外定義Person case類。 另外,在main()函數中添加import sqlContext.implicits._。
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