Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/18875#discussion_r132088249
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
---
@@ -659,13 +660,19 @@ case class StructsToJson(
(arr: Any) =>
gen.write(arr.asInstanceOf[ArrayData])
getAndReset()
+ case MapType(_: DataType, _: StructType, _: Boolean) =>
+ (map: Any) =>
+ val mapType = child.dataType.asInstanceOf[MapType]
+ gen.write(map.asInstanceOf[MapData], mapType)
+ getAndReset()
}
}
override def dataType: DataType = StringType
override def checkInputDataTypes(): TypeCheckResult = child.dataType
match {
- case _: StructType | ArrayType(_: StructType, _) =>
+ case _: StructType | ArrayType(_: StructType, _) |
+ MapType(_: DataType, _: StructType, _: Boolean) =>
--- End diff --
I see. Looks now we have assumption that `JacksonGenerator` only takes
`StructType` now. I think expression name should be fine and I guess we are
okay to rename it if it looks required (actually I did it to `StructsToJson` :)
).
Would it be difficult to support `MapType` like `StructType`? I took a
quick look and it looks quite a lot of places to fix though. Up to my
understanding, we could load JSON both `MapType` and `StructType` too.
```
scala> spark.read.schema("a map<string, int>").json(Seq("""{"a": {"a":
2}}""").toDS).show()
+-----------+
| a|
+-----------+
|Map(a -> 2)|
+-----------+
scala> spark.read.schema("a struct<a: int>").json(Seq("""{"a": {"a":
2}}""").toDS).show()
+---+
| a|
+---+
|[2]|
+---+
```
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