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The Federation SAIL allows multiple datasets to be virtually combined into a single dataset. The Federation SAIL combines multiple RDF stores that may exist on a remote server or are embedded in the same JVM. The Federation uses query optimizations to distribute sections of the query to different members based on the data contained in each of the members. These results are then joined together within the federation to provide the same result as if all the data was co-located within a single repository.

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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/
package org.eclipse.rdf4j.sail.federation.algebra;

import java.util.Map;

import org.eclipse.rdf4j.common.iteration.CloseableIteration;
import org.eclipse.rdf4j.model.Value;
import org.eclipse.rdf4j.query.BindingSet;
import org.eclipse.rdf4j.query.Dataset;
import org.eclipse.rdf4j.query.MalformedQueryException;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.query.QueryLanguage;
import org.eclipse.rdf4j.query.TupleQuery;
import org.eclipse.rdf4j.query.TupleQueryResult;
import org.eclipse.rdf4j.query.algebra.QueryModelVisitor;
import org.eclipse.rdf4j.query.algebra.TupleExpr;
import org.eclipse.rdf4j.query.algebra.UnaryTupleOperator;
import org.eclipse.rdf4j.repository.RepositoryConnection;
import org.eclipse.rdf4j.repository.RepositoryException;
import org.eclipse.rdf4j.sail.federation.evaluation.InsertBindingSetCursor;

/**
 * Indicates that the argument should be evaluated in a particular member.
 *
 * @author James Leigh
 */
public class OwnedTupleExpr extends UnaryTupleOperator {

	private final RepositoryConnection owner;

	private TupleQuery query;

	private Map variables;

	public OwnedTupleExpr(RepositoryConnection owner, TupleExpr arg) {
		super(arg);
		this.owner = owner;
	}

	public RepositoryConnection getOwner() {
		return owner;
	}

	public void prepare(QueryLanguage queryLn, String qry, Map bindings)
			throws RepositoryException, MalformedQueryException {
		assert this.query == null;
		this.query = owner.prepareTupleQuery(queryLn, qry);
		this.variables = bindings;
	}

	public boolean hasQuery() {
		return query != null;
	}

	public CloseableIteration evaluate(Dataset dataset, BindingSet bindings)
			throws QueryEvaluationException {
		CloseableIteration rval = null;
		if (query != null) {
			try {
				synchronized (query) {
					for (String name : variables.keySet()) {
						if (bindings.hasBinding(name)) {
							Value value = bindings.getValue(name);
							query.setBinding(variables.get(name), value);
						} else {
							query.removeBinding(variables.get(name));
						}
					}
					query.setDataset(dataset);
					TupleQueryResult result = query.evaluate();
					rval = new InsertBindingSetCursor(result, bindings);
				}
			} catch (IllegalArgumentException e) { // NOPMD
				// query does not support BNode bindings
			}
		}
		return rval;
	}

	@Override
	public  void visit(QueryModelVisitor visitor) throws X {
		visitor.meetOther(this);
	}

	@Override
	public String getSignature() {
		return this.getClass().getSimpleName() + " " + owner.toString();
	}

}