jena-arq/src/main/java/org/apache/jena/sparql/core/DatasetGraphMapLink.java

/*
 * 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.jena.sparql.core;

import java.util.HashMap ;
import java.util.Iterator ;
import java.util.Map ;

import org.apache.jena.graph.Graph ;
import org.apache.jena.graph.Node ;
import org.apache.jena.query.ReadWrite ;
import org.apache.jena.query.TxnType;
import org.apache.jena.sparql.SystemARQ ;
import org.apache.jena.sparql.core.DatasetGraphFactory.GraphMaker ;
import org.apache.jena.sparql.graph.GraphUnionRead ;
import org.apache.jena.sparql.graph.GraphZero;

/** Implementation of a DatasetGraph as an extensible set of graphs where graphs are held by reference.
 *  Care is needed when manipulating their contents
 *  especially if they are also in another {@code DatasetGraph}.
 *  <p> 
 *  See {@link DatasetGraphMap} for an implementation that copies graphs
 *  and so providing better isolation.
 *  <p>
 *  This class is best used for creating views  
 *  
 *  @see DatasetGraphMap
 */
public class DatasetGraphMapLink extends DatasetGraphCollection
{
    private final GraphMaker graphMaker ;
    private final Map<Node, Graph> graphs = new HashMap<>() ;

    private Graph defaultGraph ;
    private final Transactional txn;
    private final TxnDataset2Graph txnDsg2Graph;
    private static GraphMaker dftGraphMaker = DatasetGraphFactory.graphMakerMem;

    /**
     * Create a new {@code DatasetGraph} that copies the dataset structure of default
     * graph and named graph and links to the graphs of the original {@code DatasetGraph}.
     * Any new graphs needed are separate from the original dataset and created in-memory. 
     */
    public static DatasetGraph cloneStructure(DatasetGraph dsg) {
        return cloneStructure(dsg, dftGraphMaker);
    }
    
    /**
     * Create a new {@code DatasetGraph} that copies the dataset structure of default
     * graph and named graph and links to the graphs of the original {@code DatasetGraph}
     * Any new graphs needed are separate from the original dataset and created according
     * to the {@link GraphMaker}.
     */
    public static DatasetGraph cloneStructure(DatasetGraph dsg, GraphMaker graphMaker) {
        DatasetGraphMapLink dsg2 = new DatasetGraphMapLink((Graph)null, graphMaker);
        linkGraphs(dsg, dsg2);
        return dsg2;
    }

    private static void linkGraphs(DatasetGraph srcDsg, DatasetGraphMapLink dstDsg) {
        dstDsg.defaultGraph = srcDsg.getDefaultGraph();
        for ( Iterator<Node> names = srcDsg.listGraphNodes() ; names.hasNext() ; ) {
            Node gn = names.next() ;
            dstDsg.addGraph(gn, srcDsg.getGraph(gn)) ;
        }
    }

    /** A {@code DatasetGraph} that uses the given graph for the default graph
     *  and create in-memory graphs for named graphs as needed
     */
    public DatasetGraphMapLink(Graph dftGraph) {
        this(dftGraph, dftGraphMaker);
    }

    // This is the root constructor. 
    /*package*/DatasetGraphMapLink(Graph dftGraph, GraphMaker graphMaker) {
        this.graphMaker = graphMaker;
        this.defaultGraph = dftGraph;
        txnDsg2Graph = new TxnDataset2Graph(dftGraph);
        txn = txnDsg2Graph;
    }

    @Override
    public void commit() {
        if ( txnDsg2Graph == null )
            SystemARQ.sync(this);
        txn.commit() ;
    }

    @Override public void begin()                       { txn.begin(); }
    @Override public void begin(TxnType txnType)        { txn.begin(txnType); }
    @Override public void begin(ReadWrite mode)         { txn.begin(mode); }
    @Override public boolean promote(Promote txnType)   { return txn.promote(txnType); }
    //Above: commit()
    @Override public void abort()                       { txn.abort(); }
    @Override public boolean isInTransaction()          { return txn.isInTransaction(); }
    @Override public void end()                         { txn.end(); }
    @Override public ReadWrite transactionMode()        { return txn.transactionMode(); }
    @Override public TxnType transactionType()          { return txn.transactionType(); }
    @Override public boolean supportsTransactions()     { return true; }
    @Override public boolean supportsTransactionAbort() { return false; }
    // ----

    @Override
    public boolean containsGraph(Node graphNode) {
        if ( Quad.isDefaultGraph(graphNode) || Quad.isUnionGraph(graphNode) )
            return true;
        return graphs.containsKey(graphNode);
    }

    @Override
    public Graph getDefaultGraph() {
        return defaultGraph;
    }

    @Override
    public Graph getGraph(Node graphNode) {
        // Same as DatasetGraphMap.getGraph but we inherit differently.
        if ( Quad.isUnionGraph(graphNode) ) 
            return new GraphUnionRead(this) ;
        if ( Quad.isDefaultGraph(graphNode))
            return getDefaultGraph() ;
        // Not a special case.
        Graph g = graphs.get(graphNode);
        if ( g == null ) {
            g = getGraphCreate(graphNode);
            if ( g != null )
                addGraph(graphNode, g);
        }
        return g;
    }

    /**
     * Called from getGraph when a nonexistent graph is asked for.
     * Return null for "nothing created as a graph"
     */
    protected Graph getGraphCreate(Node graphNode) {
        return graphMaker.create(graphNode) ;
    }

    @Override
    public void addGraph(Node graphName, Graph graph) {
        if ( txnDsg2Graph != null )
            txnDsg2Graph.addGraph(graph);
        graphs.put(graphName, graph);
    }

    @Override
    public void removeGraph(Node graphName) {
        Graph g = graphs.remove(graphName);
        if ( g != null && txnDsg2Graph != null )
            txnDsg2Graph.removeGraph(g);
    }

    @Override
    public void setDefaultGraph(Graph g) {
        if ( g == null )
            // Always have a default graph of some kind.
            g = GraphZero.instance();
        if ( txnDsg2Graph != null )
            txnDsg2Graph.addGraph(g);
        defaultGraph = g;
    }

    @Override
    public Iterator<Node> listGraphNodes() {
        return graphs.keySet().iterator();
    }

    @Override
    public long size() {
        return graphs.size();
    }

    @Override
    public void close() {
        defaultGraph.close();
        for ( Graph graph : graphs.values() )
            graph.close();
        super.close();
    }
}