可以检索RDF4J事务的update语句吗？

Question

我正在尝试使用RDF4J支持SPARQL update查询的“预演”功能。我想通知用户将要插入/删除的语句，理想情况下是通过从当前事务中获取语句。我的想法是这样的：

conn.begin();
Update query = conn.prepareUpdate(queryString);
query.execute();
// Print statements in the transaction
System.out.println("Dry run completed.");
conn.rollback();
System.out.println("Dry run rolled back.");

有没有办法用RDF4J做到这一点？

Answer 1

(从https://github.com/eclipse/rdf4j/discussions/3163复制)

您可以使用SailConnectionListener按照这些思路做一些事情。然而，访问它的方法有点笨拙。下面是一个例子：

Repository rep = new SailRepository(new MemoryStore());
try (SailRepositoryConnection conn = (SailRepositoryConnection) rep.getConnection()) {
    NotifyingSailConnection sailConn = (NotifyingSailConnection) conn.getSailConnection();
    sailConn.addConnectionListener(new SailConnectionListener() {

        @Override
        public void statementRemoved(Statement removed) {
            System.out.println("removed: " + removed);
        }

        @Override
        public void statementAdded(Statement added) {
            System.out.println("added: " + added);
        }
    });

    conn.begin();
    conn.add(FOAF.PERSON, RDF.TYPE, RDFS.CLASS);
    String update = "DELETE { ?p a rdfs:Class } INSERT { ?p rdfs:label \"Person\" } WHERE { ?p a rdfs:Class }";
    conn.prepareUpdate(update).execute();
    System.out.println("executed");
    conn.rollback();
    System.out.println("transaction aborted");
}

正如您所看到的，我们需要将RepositoryConnection转换为特定类型以检索底层SailConnection，然后我们还需要将该SailConnection转换为NotifyingSailConnection，以便能够在其上注册SailConnectionListener。此侦听器将接收单个语句的pre-commit、and和removed事件。运行上述代码将产生以下控制台输出：

added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class)
removed: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class) [null]
added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/2000/01/rdf-schema#label, "Person")
executed
transaction aborted