Github user viirya commented on a diff in the pull request: https://github.com/apache/spark/pull/18875#discussion_r137975214 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/json/JacksonGenerator.scala --- @@ -193,14 +228,30 @@ private[sql] class JacksonGenerator( * * @param row The row to convert */ - def write(row: InternalRow): Unit = writeObject(writeFields(row, schema, rootFieldWriters)) + def write(row: InternalRow): Unit = dataType match { + case st: StructType => + writeObject(writeFields(row, st, rootFieldWriters)) + case _ => throw new UnsupportedOperationException( + s"`JacksonGenerator` can only be used to write out a row when initialized with `StructType`.") + } /** - * Transforms multiple `InternalRow`s to JSON array using Jackson + * Transforms multiple `InternalRow`s or `MapData`s to JSON array using Jackson * - * @param array The array of rows to convert + * @param array The array of rows or maps to convert */ def write(array: ArrayData): Unit = writeArray(writeArrayData(array, arrElementWriter)) + /** + * Transforms a `MapData` to JSON object using Jackson + * + * @param map a map to convert + */ + def write(map: MapData): Unit = dataType match { + case mt: MapType => writeObject(writeMapData(map, mt, mapElementWriter)) + case _ => throw new UnsupportedOperationException( --- End diff -- Similar to https://github.com/apache/spark/pull/18875/files#r137975134, we can avoid this. Doing pattern matching per writing seems too burden.
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