[jira] [Created] (SPARK-3572) Support register UserType in SQL

["Xiangrui Meng (JIRA)" <ji...@apache.org>]

Xiangrui Meng created SPARK-3572:
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             Summary: Support register UserType in SQL
                 Key: SPARK-3572
                 URL: https://issues.apache.org/jira/browse/SPARK-3572
             Project: Spark
          Issue Type: New Feature
          Components: SQL
            Reporter: Xiangrui Meng


If a user knows how to map a class to a struct type in Spark SQL, he should be able to register this mapping through sqlContext and hence SQL can figure out the schema automatically.

{code}
trait RowSerializer[T] {
  def dataType: StructType
  def serialize(obj: T): Row
  def deserialize(row: Row): T
}

sqlContext.registerUserType[T](clazz: classOf[T], serializer: classOf[RowSerializer[T]])
{code}

In sqlContext, we can maintain a class-to-serializer map and use it for conversion. The serializer class can be embedded into the metadata, so when `select` is called, we know we want to deserialize the result.

{code}
sqlContext.registerUserType(classOf[Vector], classOf[VectorRowSerializer])
val points: RDD[LabeledPoint] = ...
val features: RDD[Vector] = points.select('features).map { case Row(v: Vector) => v }
{code}



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