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Pig adapter for Calcite
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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.calcite.adapter.pig;

import org.apache.calcite.plan.RelOptCluster;
import org.apache.calcite.plan.RelOptTable;
import org.apache.calcite.plan.RelOptUtil;
import org.apache.calcite.plan.RelTraitSet;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Join;
import org.apache.calcite.rel.core.JoinRelType;
import org.apache.calcite.rex.RexCall;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.SqlKind;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;

import java.util.ArrayList;
import java.util.List;

/** Implementation of {@link org.apache.calcite.rel.core.Join} in
 * {@link PigRel#CONVENTION Pig calling convention}. */
public class PigJoin extends Join implements PigRel {

  /** Creates a PigJoin. */
  public PigJoin(RelOptCluster cluster, RelTraitSet traitSet, RelNode left, RelNode right,
      RexNode condition, JoinRelType joinType) {
    super(cluster, traitSet, ImmutableList.of(), left, right, condition,
        ImmutableSet.of(), joinType);
    assert getConvention() == PigRel.CONVENTION;
  }

  @Override public Join copy(RelTraitSet traitSet, RexNode conditionExpr, RelNode left,
      RelNode right, JoinRelType joinType, boolean semiJoinDone) {
    return new PigJoin(getCluster(), traitSet, left, right, conditionExpr, joinType);
  }

  @Override public void implement(Implementor implementor) {
    implementor.visitChild(0, getLeft());
    implementor.visitChild(0, getRight());
    implementor.addStatement(getPigJoinStatement(implementor));
  }

  /**
   * The Pig alias of the joined relation will have the same name as one from
   * the left side of the join.
   */
  @Override public RelOptTable getTable() {
    return getLeft().getTable();
  }

  /**
   * Constructs a Pig JOIN statement in the form of
   *    * {@code
   * A = JOIN A BY f1 LEFT OUTER, B BY f2;
   * }
   * 
   * Only supports simple equi-joins with single column on both sides of
   * =.
   */
  private String getPigJoinStatement(Implementor implementor) {
    if (!getCondition().isA(SqlKind.EQUALS)) {
      throw new IllegalArgumentException("Only equi-join are supported");
    }
    List operands = ((RexCall) getCondition()).getOperands();
    if (operands.size() != 2) {
      throw new IllegalArgumentException("Only equi-join are supported");
    }
    List leftKeys = new ArrayList<>(1);
    List rightKeys = new ArrayList<>(1);
    List filterNulls = new ArrayList<>(1);
    RelOptUtil.splitJoinCondition(getLeft(), getRight(), getCondition(), leftKeys, rightKeys,
        filterNulls);

    String leftRelAlias = implementor.getPigRelationAlias((PigRel) getLeft());
    String rightRelAlias = implementor.getPigRelationAlias((PigRel) getRight());
    String leftJoinFieldName = implementor.getFieldName((PigRel) getLeft(), leftKeys.get(0));
    String rightJoinFieldName = implementor.getFieldName((PigRel) getRight(), rightKeys.get(0));

    return implementor.getPigRelationAlias((PigRel) getLeft()) + " = JOIN " + leftRelAlias + " BY "
        + leftJoinFieldName + ' ' + getPigJoinType() + ", " + rightRelAlias + " BY "
        + rightJoinFieldName + ';';
  }

  /**
   * Get a string representation of the type of join for use in a Pig script.
   * Pig does not have an explicit "inner" marker, so return an empty string in
   * this case.
   */
  private String getPigJoinType() {
    switch (getJoinType()) {
    case INNER:
      return "";
    default:
      return getJoinType().name();
    }
  }
}