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* 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,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package tdb.examples;
import org.apache.jena.atlas.iterator.Filter ;
import org.apache.jena.atlas.lib.Tuple ;
import com.hp.hpl.jena.graph.NodeFactory ;
import com.hp.hpl.jena.query.* ;
import com.hp.hpl.jena.sparql.core.DatasetGraph ;
import com.hp.hpl.jena.sparql.core.Quad ;
import com.hp.hpl.jena.sparql.sse.SSE ;
import com.hp.hpl.jena.tdb.TDB ;
import com.hp.hpl.jena.tdb.TDBFactory ;
import com.hp.hpl.jena.tdb.store.NodeId ;
import com.hp.hpl.jena.tdb.sys.SystemTDB ;
import com.hp.hpl.jena.tdb.sys.TDBInternal ;
/** Example of how to filter quads as they are accessed at the lowest level.
* Can be used to exclude daat from specific graphs.
* This mechanism is not limited to graphs - it works for properties or anything
* where the visibility of otherwise is determined by the elements of the quad.
* See <a href="http://incubator.apache.org/jena/documentation/tdb/quadfilter.html">QuadFiltering</a>
* for further details.
*/
public class ExQuadFilter
{
private static String graphToHide = "http://example/g2" ;
public static void main(String ... args)
{
// This also works for default union graph ....
TDB.getContext().setTrue(TDB.symUnionDefaultGraph) ;
Dataset ds = setup() ;
Filter<Tuple<NodeId>> filter = createFilter(ds) ;
example(ds, filter) ;
}
/** Example setup - in-memory dataset with two graphs, one triple in each */
private static Dataset setup()
{
Dataset ds = TDBFactory.createDataset() ;
DatasetGraph dsg = ds.asDatasetGraph() ;
Quad q1 = SSE.parseQuad("(<http://example/g1> <http://example/s> <http://example/p> <http://example/o1>)") ;
Quad q2 = SSE.parseQuad("(<http://example/g2> <http://example/s> <http://example/p> <http://example/o2>)") ;
dsg.add(q1) ;
dsg.add(q2) ;
return ds ;
}
/** Create a filter to exclude the graph http://example/g2 */
private static Filter<Tuple<NodeId>> createFilter(Dataset ds)
{
// Filtering operates at a very low level:
// Need to know the internal identifier for the graph name.
final NodeId target = TDBInternal.getNodeId(ds, NodeFactory.createURI(graphToHide)) ;
System.out.println("Hide graph: "+graphToHide+" --> "+target) ;
// Filter for accept/reject as quad as being visible.
// Return true for "accept", false for "reject"
Filter<Tuple<NodeId>> filter = new Filter<Tuple<NodeId>>() {
@Override
public boolean accept(Tuple<NodeId> item)
{
// Reverse the lookup as a demo
//Node n = TDBInternal.getNode(target) ;
//System.err.println(item) ;
if ( item.size() == 4 && item.get(0).equals(target) )
{
//System.out.println("Reject: "+item) ;
return false ;
}
//System.out.println("Accept: "+item) ;
return true ;
} } ;
return filter ;
}
private static void example(Dataset ds, Filter<Tuple<NodeId>> filter)
{
String[] x = {
"SELECT * { GRAPH ?g { ?s ?p ?o } }",
"SELECT * { ?s ?p ?o }",
// This filter does not hide the graph itself, just the quads associated with the graph.
"SELECT * { GRAPH ?g {} }"
} ;
for ( String qs : x )
{
example(ds, qs, filter) ;
example(ds, qs, null) ;
}
}
private static void example(Dataset ds, String qs, Filter<Tuple<NodeId>> filter)
{
System.out.println() ;
Query query = QueryFactory.create(qs) ;
System.out.println(qs) ;
QueryExecution qExec = QueryExecutionFactory.create(query, ds) ;
// Install filter for this query only.
if ( filter != null )
{
System.out.println("Install quad-level filter") ;
qExec.getContext().set(SystemTDB.symTupleFilter, filter) ;
}
else
System.out.println("No quad-level filter") ;
ResultSetFormatter.out(qExec.execSelect()) ;
qExec.close() ;
}
}