ProjectionIterator.java :  » RSS-RDF » sesame » org » openrdf » query » algebra » evaluation » iterator » Java Open Source

/*
 * Copyright Aduna (http://www.aduna-software.com/) (c) 1997-2007.
 *
 * Licensed under the Aduna BSD-style license.
 */
package org.openrdf.query.algebra.evaluation.iterator;

import info.aduna.iteration.CloseableIteration;
import info.aduna.iteration.ConvertingIteration;

import org.openrdf.model.Value;
import org.openrdf.query.BindingSet;
import org.openrdf.query.QueryEvaluationException;
import org.openrdf.query.algebra.Projection;
import org.openrdf.query.algebra.ProjectionElem;
import org.openrdf.query.algebra.ProjectionElemList;
import org.openrdf.query.algebra.evaluation.QueryBindingSet;

public class ProjectionIterator extends ConvertingIteration<BindingSet, BindingSet, QueryEvaluationException>
{

  /*-----------*
   * Constants *
   *-----------*/

  private final Projection projection;

  private final BindingSet parentBindings;

  /*--------------*
   * Constructors *
   *--------------*/

  public ProjectionIterator(Projection projection,
      CloseableIteration<BindingSet, QueryEvaluationException> iter, BindingSet parentBindings)
    throws QueryEvaluationException
  {
    super(iter);
    this.projection = projection;
    this.parentBindings = parentBindings;
  }

  /*---------*
   * Methods *
   *---------*/

  @Override
  protected BindingSet convert(BindingSet sourceBindings)
    throws QueryEvaluationException
  {

    return project(projection.getProjectionElemList(), sourceBindings, parentBindings);
  }

  public static BindingSet project(ProjectionElemList projElemList, BindingSet sourceBindings,
      BindingSet parentBindings)
  {
    QueryBindingSet resultBindings = new QueryBindingSet(parentBindings);

    for (ProjectionElem pe : projElemList.getElements()) {
      Value targetValue = sourceBindings.getValue(pe.getSourceName());
      if (targetValue != null) {
        // Potentially overwrites bindings from super
        resultBindings.setBinding(pe.getTargetName(), targetValue);
      }
    }

    return resultBindings;
  }
}