org.apache.flink.table.plan.util.RexNodeRewriter.scala Maven / Gradle / Ivy

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/*
 * 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 java.util.{List => JList}
import org.apache.calcite.rex._

import scala.collection.JavaConversions._
import scala.collection.JavaConverters._

object RexNodeRewriter {

  /**
    * Generates new expressions with used input fields.
    *
    * @param usedFields indices of used input fields
    * @param exps       original expression lists
    * @return new expression with only used input fields
    */
  def rewriteWithNewFieldInput(
      exps: JList[RexNode],
      usedFields: Array[Int]): JList[RexNode] = {
    // rewrite input field in expressions
    val inputRewriter = new InputRewriter(usedFields)
    exps.map(_.accept(inputRewriter)).toList.asJava
  }
}

/**
  * A RexShuttle to rewrite field accesses of RexNode.
  *
  * @param fields used input fields
  */
class InputRewriter(fields: Array[Int]) extends RexShuttle {

  /** old input fields ref index -> new input fields ref index mappings */
  private val fieldMap: Map[Int, Int] =
    fields.zipWithIndex.toMap

  override def visitInputRef(inputRef: RexInputRef): RexNode =
    new RexInputRef(refNewIndex(inputRef), inputRef.getType)

  override def visitLocalRef(localRef: RexLocalRef): RexNode =
    new RexInputRef(refNewIndex(localRef), localRef.getType)

  private def refNewIndex(ref: RexSlot): Int =
    fieldMap.getOrElse(ref.getIndex,
      throw new IllegalArgumentException("input field contains invalid index"))
}