| /** |
| * 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 tdb.examples; |
| |
| import org.apache.jena.query.*; |
| import org.apache.jena.sparql.core.DatasetGraph; |
| import org.apache.jena.system.Txn; |
| import org.apache.jena.tdb.TDBFactory; |
| |
| /** Illustration of working at the DatasetGraph level. |
| * Normally, applications work with {@link Dataset}. |
| * Occasionally, it's more convenient to work with the |
| * TDB-implemented DatasetGraph interface. |
| */ |
| public class ExTDB_Txn3 |
| { |
| public static void main(String... argv) |
| { |
| DatasetGraph dsg = TDBFactory.createDatasetGraph(); |
| |
| // Start a transaction. It starts in "read" mode and promotes to "write" mode if necessary. |
| Txn.execute(dsg, ()->{ |
| // Do some queries |
| String sparqlQueryString1 = "SELECT (count(*) AS ?count) { ?s ?p ?o }"; |
| execQuery(sparqlQueryString1, dsg); |
| }); |
| } |
| |
| public static void execQuery(String sparqlQueryString, DatasetGraph dsg) |
| { |
| // Add a dataset wrapper to conform with the query interface. |
| // This should not be very expensive. |
| Dataset dataset = DatasetFactory.wrap(dsg); |
| |
| Query query = QueryFactory.create(sparqlQueryString); |
| try ( QueryExecution qexec = QueryExecutionFactory.create(query, dataset) ) { |
| ResultSet results = qexec.execSelect(); |
| for (; results.hasNext(); ) |
| { |
| QuerySolution soln = results.nextSolution(); |
| int count = soln.getLiteral("count").getInt(); |
| System.out.println("count = "+count); |
| } |
| } |
| } |
| } |