dongjoon-hyun opened a new pull request, #565:
URL: https://github.com/apache/spark-connect-swift/pull/565
### What changes were proposed in this pull request?
This PR aims to make `DataFrame.toJSON()` return a single column named
`value`, like the Scala Spark Connect client.
```swift
- return selectExpr("to_json(struct(*))")
+ return selectExpr("to_json(struct(*)) AS value")
```
### Why are the changes needed?
The Scala Spark Connect client names the `toJSON` output column `value`.
- [Apache Spark 4.2.0 (2026-07-11)
`Dataset.toJSON`](https://github.com/apache/spark/blob/v4.2.0/sql/connect/common/src/main/scala/org/apache/spark/sql/connect/Dataset.scala#L1277-L1279)
```scala
def toJSON: Dataset[String] = {
select(to_json(struct(col("*"))).as("value")).as(StringEncoder)
}
```
The Swift client currently names the column after the expression, such as
`to_json(struct(id))`. So the column name depends on the input schema, and code
ported from Scala that refers to `value` fails.
### Does this PR introduce _any_ user-facing change?
Yes. The output column is renamed from `to_json(struct(...))` to `value`,
matching the Scala Spark Connect client. The JSON content is unchanged.
**BEFORE**
```swift
try await spark.range(2).toJSON().columns // ["to_json(struct(id))"]
```
**AFTER**
```swift
try await spark.range(2).toJSON().columns // ["value"]
try await spark.range(2).toJSON().schema // value STRING (nullable)
```
### How was this patch tested?
Pass the CIs with the updated test case. It checks the column name, the
schema (`value STRING`, nullable), unchanged JSON content, a multi-column
DataFrame, and a nested struct column.
I also tested manually with an Apache Spark 4.2.0 Spark Connect server.
```
$ swift test --no-parallel --filter DataFrameTests
...
Test run with 152 tests in 2 suites passed after 22.965 seconds.
```
### Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude Opus 5
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