Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/8889#discussion_r40339049
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/LogicalRelation.scala
---
@@ -17,23 +17,44 @@
package org.apache.spark.sql.execution.datasources
import org.apache.spark.sql.catalyst.analysis.MultiInstanceRelation
-import org.apache.spark.sql.catalyst.expressions.{AttributeMap,
AttributeReference}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeMap,
AttributeReference}
import org.apache.spark.sql.catalyst.plans.logical.{LeafNode, LogicalPlan,
Statistics}
import org.apache.spark.sql.sources.BaseRelation
/**
* Used to link a [[BaseRelation]] in to a logical query plan.
+ *
+ * Note that sometimes we need to use `LogicalRelation` to replace an
existing leaf node without
+ * changing the output attributes' IDs. The `expectedOutputAttributes`
parameter is used for
+ * this purpose.
*/
-private[sql] case class LogicalRelation(relation: BaseRelation)
- extends LeafNode
- with MultiInstanceRelation {
+private[sql] case class LogicalRelation(
+ relation: BaseRelation,
+ expectedOutputAttributes: Seq[Attribute] = Nil)
--- End diff --
Can we use `Option[Seq[Attribute]]`? I think the semantic of having a
`Option` at here is more clearer than just using a `Seq` and the meaning of it
is self-explanatory. `None` means that `expectedOutputAttributes` is not
defined.
If we use `Seq`, `Nil` does not necessarily mean that
`expectedOutputAttributes` is not defined. Without other comments, it can mean
that we have defined `expectedOutputAttributes` and it is a `Nil`. Readers have
to take a look at our comments to understand its meaning.
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