Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/17192#discussion_r106797757 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala --- @@ -624,41 +627,58 @@ case class StructToJson( lazy val writer = new CharArrayWriter() @transient - lazy val gen = - new JacksonGenerator( - child.dataType.asInstanceOf[StructType], - writer, - new JSONOptions(options, timeZoneId.get)) + lazy val gen = new JacksonGenerator( + rowSchema, writer, new JSONOptions(options, timeZoneId.get)) + + @transient + lazy val rowSchema = child.dataType match { + case st: StructType => st + case ArrayType(st: StructType, _) => st + } + + // This converts rows to the JSON output according to the given schema. + @transient + lazy val converter: Any => UTF8String = { + def getAndReset(): UTF8String = { + gen.flush() + val json = writer.toString + writer.reset() + UTF8String.fromString(json) + } + + child.dataType match { + case _: StructType => + (row: Any) => + gen.write(row.asInstanceOf[InternalRow]) + getAndReset() + case ArrayType(_: StructType, _) => + (arr: Any) => + gen.write(arr.asInstanceOf[ArrayData]) + getAndReset() + } + } override def dataType: DataType = StringType - override def checkInputDataTypes(): TypeCheckResult = { - if (StructType.acceptsType(child.dataType)) { + override def checkInputDataTypes(): TypeCheckResult = child.dataType match { + case _: StructType | ArrayType(_: StructType, _) => --- End diff -- It seems `StructType.acceptsType` and `ArrayType.acceptsType` call `isInstanceOf[StructType]` and `isInstanceOf[ArrayType]`. `isInstanceOf` and pattern matching are interchangeable in most cases up to my knowledge. (I just found a reference https://www.safaribooksonline.com/library/view/scala-cookbook/9781449340292/ch03s15.html) Namely, this case below should be fine. (Up to my knowledge, Scala forbids case-to-case inheritance BTW) ``` scala> case class A() defined class A scala> class B extends A defined class B scala> new B() match {case _: A => println(1)} 1 ```
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