FilterIterator.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 java.util.Set;

import info.aduna.iteration.CloseableIteration;
import info.aduna.iteration.FilterIteration;

import org.openrdf.query.BindingSet;
import org.openrdf.query.QueryEvaluationException;
import org.openrdf.query.algebra.Filter;
import org.openrdf.query.algebra.evaluation.QueryBindingSet;
import org.openrdf.query.algebra.evaluation.ValueExprEvaluationException;
import org.openrdf.query.algebra.evaluation.EvaluationStrategy;

public class FilterIterator extends FilterIteration<BindingSet, QueryEvaluationException> {

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

  private final Filter filter;

  private final EvaluationStrategy strategy;

  /**
   * The set of binding names that are "in scope" for the filter. The filter
   * must not include bindings that are (only) included because of the
   * depth-first evaluation strategy in the evaluation of the constraint.
   */
  private final Set<String> scopeBindingNames;

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

  public FilterIterator(Filter filter, CloseableIteration<BindingSet, QueryEvaluationException> iter,
      EvaluationStrategy strategy)
    throws QueryEvaluationException
  {
    super(iter);
    this.filter = filter;
    this.strategy = strategy;
    this.scopeBindingNames = filter.getBindingNames();
  }

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

  @Override
  protected boolean accept(BindingSet bindings)
    throws QueryEvaluationException
  {
    try {
      // Limit the bindings to the ones that are in scope for this filter
      QueryBindingSet scopeBindings = new QueryBindingSet(bindings);
      scopeBindings.retainAll(scopeBindingNames);

      return strategy.isTrue(filter.getCondition(), scopeBindings);
    }
    catch (ValueExprEvaluationException e) {
      // failed to evaluate condition
      return false;
    }
  }
}