TransformBase.java

/*
 * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
 *
 * Licensed 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.gradoop.flink.model.impl.operators.transformation.functions;

import org.apache.flink.api.common.functions.MapFunction;
import org.gradoop.common.model.api.entities.Element;
import org.gradoop.flink.model.api.functions.TransformationFunction;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Initializes the current version and executes the transformation function.
 *
 * @param <EL> EPGM element type
 */
public abstract class TransformBase<EL extends Element>
  implements MapFunction<EL, EL> {

  /**
   * EPGMElement modification function
   */
  private final TransformationFunction<EL> transformationFunction;

  /**
   * Constructor
   *
   * @param transformationFunction element modification function
   */
  protected TransformBase(TransformationFunction<EL> transformationFunction) {
    this.transformationFunction = checkNotNull(transformationFunction);
  }

  /**
   * Applies the modification function on the current element and its copy.
   *
   * @param element current element
   * @return modified element
   * @throws Exception on failure
   */
  @Override
  public EL map(EL element) throws Exception {
    return transformationFunction.apply(element, initFrom(element));
  }

  /**
   * Initializes the new element from the current element.
   *
   * @param element current element
   * @return current element with identical structure but plain data
   */
  protected abstract EL initFrom(EL element);
}