Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/15354#discussion_r85583061
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
---
@@ -494,3 +495,46 @@ case class JsonToStruct(schema: StructType, options:
Map[String, String], child:
override def inputTypes: Seq[AbstractDataType] = StringType :: Nil
}
+
+/**
+ * Converts a [[StructType]] to a json output string.
+ */
+case class StructToJson(options: Map[String, String], child: Expression)
+ extends Expression with CodegenFallback with ExpectsInputTypes {
+ override def nullable: Boolean = true
+
+ @transient
+ lazy val writer = new CharArrayWriter()
+
+ @transient
+ lazy val gen =
+ new JacksonGenerator(child.dataType.asInstanceOf[StructType], writer)
+
+ override def dataType: DataType = StringType
+ override def children: Seq[Expression] = child :: Nil
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ if (StructType.acceptsType(child.dataType)) {
+ try {
--- End diff --
Sorry, one final comment as I'm looking at this more closely. I don't
think we should use exceptions for control flow in the common case.
Specifically, `verifySchema` should work the same way as `acceptsType` above
and return a boolean.
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