rdblue commented on a change in pull request #24812: [SPARK-27965][SQL] Add
extractors for v2 catalog transforms.
URL: https://github.com/apache/spark/pull/24812#discussion_r291267229
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalog/v2/expressions/expressions.scala
##########
@@ -111,32 +122,104 @@ private[sql] final case class ApplyTransform(
override def toString: String = describe
}
+/**
+ * Convenience extractor for any Literal.
+ */
+private object Lit {
+ def unapply[T](literal: Literal[T]): Some[(T, DataType)] = {
+ Some((literal.value, literal.dataType))
+ }
+}
+
+/**
+ * Convenience extractor for any NamedReference.
+ */
+private object Ref {
+ def unapply(named: NamedReference): Some[Seq[String]] = {
+ Some(named.fieldNames)
+ }
+}
+
+/**
+ * Convenience extractor for any Transform.
+ */
+private object NamedTransform {
+ def unapply(transform: Transform): Some[(String, Seq[Expression])] = {
+ Some((transform.name, transform.arguments))
+ }
+}
+
private[sql] final case class IdentityTransform(
ref: NamedReference) extends SingleColumnTransform(ref) {
override val name: String = "identity"
override def describe: String = ref.describe
}
+private[sql] object IdentityTransform {
+ def unapply(transform: Transform): Option[FieldReference] = transform match {
+ case NamedTransform("identity", Seq(Ref(parts))) =>
+ Some(FieldReference(parts))
+ case _ =>
+ None
+ }
+}
Review comment:
Yes, we need them.
The idea is to make any transform that is equivalent to an
`IdentityTransform(...)` instance of Spark's case class work in a `match`
expression as though it were actually an `IdentityTransform` instance. That
way, Spark can internally use these case classes, even though users may pass
instances that are unknown classes. This will reduce future bugs caused by
matching `IdentityTransform` instead of remembering to match the more general
`NamedTransform("identity", ...)`.
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