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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * 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.druid.segment.virtual;

import com.google.common.base.Preconditions;
import org.apache.druid.math.expr.Expr;
import org.apache.druid.math.expr.ExprEval;
import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector;
import org.apache.druid.segment.ColumnValueSelector;
import org.apache.druid.segment.RowIdSupplier;

import javax.annotation.Nullable;

/**
 * Basic expression {@link ColumnValueSelector}. Evaluates {@link Expr} into {@link ExprEval} against
 * {@link Expr.ObjectBinding} which are backed by the underlying expression input {@link ColumnValueSelector}s
 */
public class ExpressionColumnValueSelector extends BaseExpressionColumnValueSelector
{
  private final Expr.ObjectBinding bindings;
  private final Expr expression;

  public ExpressionColumnValueSelector(
      Expr expression,
      Expr.ObjectBinding bindings,
      @Nullable RowIdSupplier rowIdSupplier
  )
  {
    super(rowIdSupplier);
    this.bindings = Preconditions.checkNotNull(bindings, "bindings");
    this.expression = Preconditions.checkNotNull(expression, "expression");
  }

  @Override
  protected ExprEval eval()
  {
    return expression.eval(bindings);
  }

  @Override
  public void inspectRuntimeShape(RuntimeShapeInspector inspector)
  {
    super.inspectRuntimeShape(inspector);
    inspector.visit("expression", expression);
    inspector.visit("bindings", bindings);
  }
}