cloud-fan commented on a change in pull request #26969: [SPARK-30319][SQL] Add
a stricter version of `as[T]`
URL: https://github.com/apache/spark/pull/26969#discussion_r366331841
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
##########
@@ -495,6 +495,25 @@ class Dataset[T] private[sql](
select(newCols : _*)
}
+ /**
+ * Returns a new Dataset where each record has been mapped on to the
specified type.
+ * This only supports `U` being a class. Fields for the class will be mapped
to columns of the
+ * same name (case sensitivity is determined by `spark.sql.caseSensitive`).
+ *
+ * If the schema of the Dataset does not match the desired `U` type, you can
use `select`
+ * along with `alias` or `as` to rearrange or rename as required.
+ *
+ * This method eagerly projects away any columns that are not present in the
specified class.
+ * It further guarantees the order of columns as well as data types to match
`U`.
+ *
+ * @group basic
+ * @since 3.0.0
+ */
+ def toDS[U : Encoder]: Dataset[U] = {
+ val columns = implicitly[Encoder[U]].schema.fields.map(f =>
col(f.name).cast(f.dataType))
Review comment:
This doesn't work even for simple classes when the encoder is
`Encoders.javaSerialization`. I agree that this is a valid use case, and people
can create a Util function to do it. But I don't agree this is general enough
to be put in a method named `toDS`.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
With regards,
Apache Git Services
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
