flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/util/SameRelObjectShuttle.scala

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.flink.table.plan.util

import com.google.common.collect.Sets
import org.apache.calcite.rel.RelNode

import scala.collection.JavaConversions._

/**
  * Rewrite same rel object to different rel objects.
  *
  * <p>e.g.
  * {{{
  *      Join                       Join
  *     /    \                     /    \
  * Filter1 Filter2     =>     Filter1 Filter2
  *     \   /                     |      |
  *      Scan                  Scan1    Scan2
  * }}}
  * After rewrote, Scan1 and Scan2 are different object but have same digest.
  */
class SameRelObjectShuttle extends DefaultRelShuttle {
  private val visitedNodes = Sets.newIdentityHashSet[RelNode]()

  override def visit(node: RelNode): RelNode = {
    val visited = !visitedNodes.add(node)
    var change = false
    val newInputs = node.getInputs.map {
      input =>
        val newInput = input.accept(this)
        change = change || (input ne newInput)
        newInput
    }
    if (change || visited) {
      node.copy(node.getTraitSet, newInputs)
    } else {
      node
    }
  }
}